 Thanks, Hope. Hi, everyone. I'm Kristen Lace from Heritage Preservation, and welcome back to the Caring for Yesterday's Treasures today online course. This is our first course that we're offering, Collections Care Basics, Where Do I Begin? And we wanted to thank, again, IMLS, the Institute of Museum and Library Services, for making grant funds available for this series through their Laura Bush 21st Century Librarian Grant. And we want to thank Learning Times, especially Hope, for helping us produce these webinars. Again, as Hope mentioned, we hope you are hearing us well, and thank you for saying hello in our chat box to the left of the screen. We're going to actually, in a minute, I'm going to close that and drag it away. But feel free to continue to type in questions for us. We will be watching for those questions and comments. And if it has to do with, like, tech issues or a logistical question, we'll just answer you privately. But if it has to do with the topic we're discussing today, we'll go ahead and publish it. So if you don't see your question in print, don't panic. We are reading it, and we will answer you one way or the other. I just wanted to give you a few tips on some tech issues that we had yesterday, just a few troubleshooting tips. If you're having trouble with sound, you may want to close some of the other programs on your screen that you might have running on your computer right now. Don't close your browser, because you might log out of this. But that's one thing that tends to help people. If you're hearing an echo, you may have mistakenly logged in twice, so double check for that. And if you're still having any trouble, hopefully the closed captioning helps with this issue. Sometimes if you're on a wireless network, if the network is a little spotty, the sound could cut in and out. Also, I want to just let you know, again, that I'm going to drag this chat away. I don't mean to cut anybody off, but I'm going to drag this away, and you will see our Q&A box that we will use today during our session. All right, there it goes. Today we are discussing Collections Environment, and we hope you joined us yesterday for our overview on Agents of Deterioration. And we had a lot of questions yesterday about the environment, and I want to let you know we passed those along to our instructor, and we hopefully will get to all of them today. And we've gotten such great interest in this course. We're so pleased to have all of you here. We've already got almost 300 again logged in today, as we did yesterday. We have a couple of poll questions about who you are. We asked you a few yesterday, and I want to check and see where folks are coming from today. Yesterday we asked what type of institution you work at, and today I thought it would be interesting to know where people are attending from. We've had a number of overseas participants are interested from people overseas. Oh, I'm going to make this a little larger, sorry. Hold on a sec. Yes. I don't think anyone is up late in Australia, but just in case, or up early. I'm not even sure what it might be. But it looks like we have nice diversity from around the country, and little in Canada. And hello to anyone who's coming in from Europe and Central America, or Africa. That's very, very cool. Okay. I think I'm going to drag this poll away, but also we wanted to welcome people who are, we have a number of students who are participating, and a lot of employees of colleges and universities just thought we'd ask a quick poll question to those folks if you want to tell us a little bit about yourself. And some of you aren't associated with colleges and universities. I wanted to give a shout out to those that are. Great. So a couple of grad students hanging in there, and a number of employees at universities too. Well, thanks for that. And we'll be asking similar questions as the week goes on, or I should say as this course goes on. Okay, I'm just going to drag this away. And we had some really great questions yesterday, and in fact some of them have inspired a discussion on our online community. So if you haven't yet joined the Connecting to Collections online community, it's the same website that you went to to register for these courses. Connecting to Collections.org. And this is just another great way to interact with us and your colleagues. You have a lot of conservators that are members of the community, which is wonderful, and a lot of them are good at chiming in and giving advice and giving information. We have lots of links to topics of interest and webinars that we've done. Oh gosh, two dozen at least. A variety of topics, and you'll find links to all of those on the online community. So we've really designed this to be sort of a one-stop shop for reputable information about conservation and preservation. And we hope that you'll make the most of it. I wanted to just also reiterate this course and the fact that we're offering a certificate of completion. So if you tend all of our six webinars and complete all of our homework assignment for this Collections Care Basics course, you'll earn a certificate of completion. And don't panic if you have to miss a webinar. You can watch that on your own time. Hopefully you got our email yesterday with a link to yesterday's webinar. And we will do the same after this webinar concludes. Probably send it out tomorrow to everyone. And if for whatever reason you didn't receive it, feel free to just drop us a note at info at heritagepreservation.org. And you don't have to work towards a certificate, but hopefully it's helpful to you. And we just ask that you either watch all the webinars and do all the homework no later than January 31 so that we can just sort of keep on track with everything. Again, there's a page for this whole course connecting to Collections.org. It's the home page and then click on courses and then Collections Care Basics and you will have links to the homework, lots of readings that our speakers have thought of in advance. Things came up in yesterday's conversation like that cocktail recipe. We put that up. So we're constantly updating and proving this page. So keep coming back to it. And then just another note on homework. We're trying to get it all done by January 31. Today's homework is actually a quiz, but don't panic. You don't have to earn 100% to get credit. We're not going to tell you how you did score just because we don't...we can't... There's 300 of you guys, so we can't provide individual feedback, but we'll tell the group how you guys did. And I think the questions are fairly straightforward. It just gives us a chance for our instructors to get a sense that the concepts they're sharing are really sinking in with the group. So without further ado... Oh, yes. If you are a certified archivist, you can earn up to five continuing credits, education credits for this course. So don't forget about that. And I want to introduce our speaker for today. It's Tara Kennedy. She is a paper conservator and a preservation field services librarian at Yale University. And she does consulting on preservation throughout the country, and she's got over a decade of experience. She recently did a really great webinar for us on the Connecting to Collections online community that deals with odors in collections. So let's not ask her a lot of questions about that today, but I can post the link, and it was really useful one-hour webinar where she had answered a lot of interesting questions on that issue. So I will turn it over to Tara. But again, if during the presentation you have questions or comments, just type it into the Q&A box to the left of the screen, and we'll get back to you. So Tara, I'm going to drag up your presentation and get you going. Okay, great. Thanks, Kristen. Hi, everyone. I'm Tara Kennedy, and I am representing myself as a preservation consultant today. But as Kristen mentioned, during my nine to five life, I am the preservation field services librarian at Yale University Library. So I just want to tell you a little bit about what we'll be talking about today. So the purpose of this lecture overall is to convey the importance of the effects of light, temperature, relative humidity, and pollutants on collection objects. On top of that, I'm also going to talk about some practical information and solutions to solving issues that you may be having in your collections in terms of environment. It's divided into three sections. One's on light, one's on relative humidity and temperature, and the other's on pollutants. So I'll be pausing in between the sections for any questions about the section that you may have. And of course, I can take all of your questions at the end as well. And Kristen, as she mentioned, was kind enough to send some of your questions along to me that pertain to temperature, relative humidity, and that sort of thing. So hopefully I will be able to answer those for you as well as we go along. All right. Let's see if I can get this to go. Okay, there it goes. It was just thinking about it. So our first section's on light. So I'm going to talk a little bit about what light is. So light is energy that's on a certain part of the wavelength spectrum. So the parts that I'm going to talk about are from about 180 nanometers to 850 nanometers. And nanometer is simply how we express measurement in light in terms of wavelengths. Next slide. So beyond the blue light is ultraviolet light. We can't see this, but UV light has a lot of energy. And this is the element of light that burns our skin when we go hang out on the beach. It is in the range of 180 nanometers to 390 nanometers. And above UV wavelengths are higher energy wavelengths like X-rays and then gamma radiation, which are, as I mentioned, higher energy and more damaging than ultraviolet. Next slide. And beyond the red portion of the light spectrum is infrared. Again, we can't see this either, but we feel it is heat. So this is lower energy than other parts of the spectrum. It is about a range from 760 nanometers to 880 nanometers. And these are lower energy wavelengths than infrared include microwave and radio waves. Next. And in the visible range is 400 to 760 nanometers. And this is the light that we can see and we need in order to see. So this is most relevant to us in terms of the collection environment. Next slide. So a couple things to keep in mind. When you are lighting a room, lighting a display, you don't need ultraviolet light or infrared. These are not needed to perceive color at all. So you want to eliminate these two as much as you can in especially the exhibit environment and as much as you can in the collections environment just in say a reading room, that sort of thing. Because you want to expose your material to as little of these light sources as possible, especially ultraviolet because it is so high energy and so damaging. But the one thing I want everyone to keep in mind is that all types of light will cause damage. Whether that be visible, ultraviolet light or infrared, all of these will cause some sort of damage in your collections. So the other thing to also note is the same amount of damage is going to occur whether it's a little bit of light over a very long period of time or a lot of light in a very short period of time. And I'll talk a little bit about what our recommended levels are in terms of when you want to have something on display and that sort of thing. Next slide. So what does light do to objects? So many objects that are in our collections have colorants as part of their overall makeup. So in chemistry land and conservation land we call coloring groups chromophores, as it shows there. So chromophores or coloring groups have, chemically speaking, have double bonds as part of their inherent chemical composition. So chemical reactions occur from light energy and acidic degradation break up these double bonds, like they're showing here in this illustration here. So once the double bond is broken after chemical attack, then it ends up changing the color of something. So when you see something that's faded or something that's yellowed or something that's changed color over time when it's been exposed to light, that's what's happening. Double bonds are breaking and it's altering the color because the way the light reflects on the object and how you're seeing it is changed because the chemical makeup of the actual chromophore has changed. It's cool. Chemistry is cool. Next slide. So here's an example of what light can do over time. So what we have here on the left, they're both images, by the way, that were taken in a conservation context. This is for photo documentation. So these are good quality photographs that we're looking at here. So the image on the left is a painting on canvas called Echo by Jackson Pollock from 1987. And then the image on the right here is the same painting in 2012. So Echo has been described as a piece from the Pollock Black and White series, but now it would be better described as a piece from his Black and Straw Yellow series, as you can see that the overall canvas is yellowed over time. So canvas is made up of organic fibers that have deteriorated partially due to light and heat, energy that has broken down the fibers and changed how the light absorbs it, thus giving it a yellow appearance rather than its white appearance as it was before. So this is just sort of a practical example of what happens in terms of color change and what light energy can do to organic materials. Next slide, please. So, as I mentioned, total light, well, sort of mentioned, total lifetime exposure is what's the most important factor when it comes to light. Next. And that can be essentially described in this very simple calculation, which total exposure would equal the intensity of the light times the amount of time that it's on display or it's been exposed to light. So if you consider that a sun is about 10 to 15,000 lux in just one measurement, it kind of makes people think twice about using natural light as a method of using, as a method of lighting up a display or something like that, because it's incredibly high energy. Next. And the other thing I'd like to note is that fading and color change cannot be reversed. Next slide. Here's an example of a fading problem. A client brought me this certificate and wanted me to restore the ink that's faded. They had it displayed in a not very bright part of their home and there was writing here, here, here. It's a baptismal certificate and you can sort of see it here. And the person wanted me to bring back the ink. I think she had been watching too many CSI shows, something along those lines. So I had to explain to her that once ink has faded, it is not reversed. It can't be brought back. You can use alternate light sources to show where the ink may have been in some cases, but you can't actually restore it sort of taking a marker and tracing over where it is and nobody wants to be doing that to their objects. So I just wanted to kind of give an example of what can happen. Even when you don't have things in direct sunlight or direct light, things still can fade. Inks can be incredibly fugitive, so it's something to be aware of and something to take into account when you put items on display. Next. Okay, so I'll talk a little bit about the different kinds of artificial light sources that are available to you that you can use whether you're in a, whether it's in a display environment or just in your general room where you're doing work. Incandescent lights are the oldest style of lights that have been available. They have low UV, but they emit a lot of heat because the way the light source is created is there's a filament inside that bulb, which is heated up, and that's how the light is created. So if you do want to use incandescent light, you want to make sure your light source, the bulb itself, is far away from your objects, especially, and you don't want it somehow in a case or anything like that because heat would build up very quickly. Next. Halogen lights, they're kind of the worst of both worlds, unfortunately. They have ultraviolet and infrared, so you really need to, you need to filter them for ultraviolet if you do use them in your collection environment, and you want to keep them far away from objects as well so they don't heat, add heat. Next. Fluorescent lights, and this is a pretty common light that you're probably seeing these days, mostly because they are low energy, especially the compact fluorescent lamps that you see here that I have in the slide there. One problem with fluorescent lights, they have a lot of ultraviolet light in them, but you can get different lamps. When I say lamp, I mean bulb. So you can get different bulbs that actually will emit lower UV emissions. General Electric, GE, makes bulbs, fluorescent tubes that are called cover guard, which I have there, that emit low UV. So those are a good choice because they are able to choose what type of bulb you have in, for light. You also, if you can't, if you don't get to choose what kind of bulbs you have in your space, you can also get these sleeves, which we use here at Yale. We have a lot of fluorescent tubing lighting and a lot of different spaces, so we found these sleeves that go on top of the bulbs that are gradient, so basically what that means is you can sort of turn these sleeves and reduce the amount of light that's emitted. It takes out UV and it also will reduce the amount of visible light, so you can make it dimmer or brighter and adjust it to whatever is actually in there in terms of display. I have links to those particular types of sleeves if you're interested in the resources, so you can go purchase them and use them yourself. One of the advantages also why fluorescent lighting is nice is they have low heat, so you don't have to worry about overheating your objects. Next, high intensity discharge. You're not going to probably see a lot of these. This is usually used in outdoor lighting. They're much too high energy, too much heat, so you're not something you're going to probably see very often. Next, fiber optics. This is something that is often used in displays. They're a very good option. They're very low ultraviolet, but they don't emit a great deal of light, so they're really best for darker spaces. The box that's attached, this is where the light source is coming from, but this is the energy source. This emits a lot of heat, so this needs to be in a space that's well ventilated. Next, LEDs, or light emitting diode lights. These are actually really making quite a splash in the exhibit world. They have no heat gain, no ultraviolet, and when they first came out, they used to kind of give this weird cast. They tended to be like a cooler color temperature. They were kind of hard to use in display because they actually didn't render very good render colors very well in the exhibit environment. Now they're actually made them in a much wider variety of color temperatures now, so it doesn't look quite so bizarre, which is nice. Next, so what do I choose? Cost, of course, will be one of the biggest factors. Some light sources are going to be less expensive than others. Light emitting diodes, LEDs, fiber optic lighting, those are going to be the more expensive options for exhibit lighting especially. So you may not be able to do those, but you can do things like, if you only have fluorescent lamps, then you can actually do sleeves, you can do, or you can get low UV bulbs, there's varieties, there's things you can actually do to reduce the possibility of damage for your collections. And application is the other thing to think about if it's a display versus you're just using it in a reading room or it's just a test lamp, so these are things you kind of have to take into consideration when you actually choose them. Next. So for measuring and monitoring light, there's a passive method, which is a pretty easy one, using blue wool standard cards. So these can be used to show accumulated damage, whether it be visible or ultraviolet light that you're measuring. Next. So here I've given you an example of ones that have been used. So this one is a, oh, come on, pointer. This is not moving. Okay, so the pointer's not working. So the card on the left is one that's not been exposed to anything. So what you do is you want to keep one that's a control. In other words, one you want to keep in the dark and never have it exposed to light, so you have something to compare it to. And then what you can do is take your, let's see if I can get it to go. No. I really want the pointer to go. Nope. Okay. So the middle one, what you see here is a piece of aluminum foil is covered the left-hand side, and a UV film is on the far right. So when they actually put it out in the exhibit case and they lift away the aluminum foil after a certain amount of time and lift away the UV sleeve over time, then you can sort of see the color difference. So you can see that the middle, without any protection at all, has some pretty significant damage. And you would compare it to the UV side. You can see that UV filtering does actually help somewhat, but not a great deal in this particular instance with the lighter colors. So in the way the scale works is the very top strip is the most fugitive, meaning it's the most likely to fade. And then all the way down at the bottom is the one that's going to be the least fugitive or the least likely to fade. Next. You can also use active methods like light meters. The light meter I'm showing there on the right is just your standard light meter that you would use in photography. And those are perfectly fine to use for measuring visible light. I use one very much like this when I go on site visits, and I have a different meter that I use to measure ultraviolet light. Next. And this one is a little more high-end model by a little more scientific. It's called an ELSEC, E-L-S-E-C. And it actually can measure visible and ultraviolet light. There's also a model that will measure infrared or heat. And it also will measure temperature and relative humidity. So it can do many things all in one. Next. So the image I'm showing here is someone who is taking an incident reading of light. And what I mean by that is they're standing in front of the object and that you want to measure the light that's actually being cast onto the object. And that's what this woman's doing here with this textile. And you can also measure light that's either reflecting off an object or a deflector or a wall, and we call that genius, a reflective reading. So. And the lifetime levels in terms of exposure and things and what things can tolerate will vary upon the type of material. Next. And this is another type of light meter that's actually one where you can place it into an exhibit case and it will measure light levels over time while just sitting there in a case. And it's unfortunately a more expensive option. So this particular Hanwell model that I'm showing here goes for $900 a piece. So, a little expensive. But, you know, you've got to see all your options before you buy, right? Next. So, and one of the other things when you're actually measuring light levels, it's really important to keep records. So that allows you to interpret changes over time in levels and the quality of light. And so, for example, if you have UV filters on your fluorescent bulbs, you can track when they need to be changed. There's some variation I've heard of in terms of how long the filters work. I've heard 15 years. I've heard longer. So it's really a good idea to get in the habit of measuring the light level to make sure that they are actively working for you. Next. So recommended display light levels. 50 lux, which is the European measurement for measuring light is lux. American is foot candles. So it's 50 lux if you're hanging out in Europe. It's five foot candles if you're in the States for light-sensitive artifacts. So light-sensitive artifacts, this means art on paper, watercolors, textiles, botanical specimens, and dyes that are especially sensitive to light. One thing to note is only 20 lux or two foot candles is necessary for the human eye to perceive color. So you really don't. It seems like it's not a lot of light, but it actually is sufficient for your eye to perceive color. So for less sensitive artifacts, then that means metals, ceramics, glass, some paintings, and some furniture, depending upon what kind of finishes it might have or any sort of colorants it might have. 50 to 200 lux or five to 20 foot candles is the maximum light levels that we recommend in conservation. And for ultraviolet, the absolute maximum, we say, is 75 microwatts per lumen. But if you can eliminate ultraviolet from your display light, that's the best recommendation we can give, because as I mentioned earlier, ultraviolet light is not necessary for the eye to be able to see. It is not part of the visual spectrum, so we do not need it. So if you can take it out, take it out. Next. So I can talk a little bit about different ways you can control light in exhibit spaces. So when I'm talking about that five foot candles, 50 lux, which seems really dark, there's ways you can control light to make the eyes make it to full the eye into thinking that it's actually brighter than it is. But in this example, so skylights, you can actually use these safely, especially if it's a directional skylight that's used as reflective light, if you bounce it off a wall and use the reflective light as a method of lighting a space, that's actually much safer because you're going to reduce the amount of energy in terms of the light levels just by bouncing it off the surface. Next. I've mentioned this a number of time filters. You can filter windows. You can put films on windows to reduce visible ultraviolet and heat. They make quite a number of them, and they can be installed professionally. You can do it yourself. They have a wide variety of different things that will actually work quite well, that actually do reduce the amount of light evenly. You can also use filters directly on your lamps or bulbs as well. You can also use them as part of your exhibit case. They'll be different things you can use to actually block UV because of the inherent material, like plexiglass. Next. Dimmers. Again, sort of common sense. It's a way to control the strength of the light being used, and if you have a light meter, you can see what level you're at, and you can actually mark it on the dimmer, so you know that that would be your five-foot candles if you happen to have your watercolors on display at that point. So then you can adjust it to that if you have watercolors, and then make a different mark if you need a different adjustment for something else that's for ceramics or something that's not quite as light-sensitive. Next. These are activated lighting systems. These are awesome. So a light wouldn't come on until someone actually enters the room. Again, this is something that's a little more of an expensive option, but it's a really great one for things that you're super worried about in terms of light levels, and light sensitivity, textiles, that sort of thing. Those I really recommend. Okay. Next. Actually, Tara, the next one gets you into relative humidity. Yay! And I wondered if you had a minute to take a break to answer some of these great light-related questions. Sure. So light bulbs have been going off, ha-ha. A couple of questions about sleeves. Can you see the list of questions I pulled aside? I see, okay. You know, these new energy-efficient bulbs, can you get sleeves for those? We have that link you shared with everyone from ErgoMart. Yes. Is that a one-stop shop for all your sleeve needs? That particular place actually does mostly lighting for theater, believe it or not, actually. So more theatrical applications. I don't know of any sleeves for compact fluorescent lamps. Donya didn't either. She mentioned that. Unfortunately. And it's one of those real... It's a bulb that a lot of places use. We use them here at Yale, and they're everywhere. And I've been trying to find something that would be applicable to filter out the UV. The one thing that people can do is when you go to choose a bulb, you do have the manufacturer's specifications, and you can actually read, now that I've told you about the spectrum and the UV spectrum, you know what nanometer is that spectra is. So if you go and look, and it will tell you what the UV spectra is or the spectra for the light bulb, what it actually is. So if it can say that it actually runs from this nanometer to that nanometer, then you'll know that how much of it is actually going to be the higher energy UV. What I mean is if you pick up a compact fluorescent, it says that it's got... The spectrum runs from like 200 to 500 nanometers. That would have a lot of UV in it because 400 and... 400 or 390 to 180 is the UV spectra. So you want to get something that's closer to 390 to 500, for example. Does that make sense? And so it's very long-winded answer. Okay. And how often should you change up, please, some fluorescence? I think they come brittle when? After a while? That's the thing. The rule of thumb has been 10 to 15 years. So it is quite a long time. What I really would recommend is either getting... somehow obtaining an ultraviolet light meter, whether you borrow one from somebody or purchase one yourself, because they make one's callus is a company that sells one just a UV meter. And if you just take light levels, measurements, every... even if you do it annually, just to make sure that the sleeves are still working, that's probably your best bet. But it's usually about 10 to 15 years. Okay. And I guess... let's see. Can an LED bulb be used in a standard halogen fixture? I don't think it can. I'm trying to remember what we have in the exhibit cases. No, I don't think it can, because I think it needs... no, I don't think it can. Okay. I think we're also getting a question about the filtering on windows. If you've got that going on, let's see. It says if a building has windows that have been treated with UV filtering, should there be a concern about visible light damage? Yes. UV filtering means that it's only filtering those particular nanometers that I mentioned, 180 to 390. You're still going to have to worry about 400 to, I think it was 760. So visible light is going to be a different part of the spectra than what that filtering is going to be. So if you can see light coming through that, then there's going to be visible light damage. But it's not going to be as high energy as if it were with the UV, because the UV is the most damaging. But all types of light will be a concern. Right. And then how often should you check light levels? I mean, you said check them pretty regularly just to make sure your filters are still effective. But all things being equal. Yeah. If you're, anytime you change and exhibit out, so if you're going to refocus your lights and things like that, you definitely want to do that. If you've changed your bulbs at any point, you want to check your light levels. Otherwise, light surveys can be done quarterly four times a year. That's usually what I, that's usually the recommendation I make. Okay. I've had a lot of good questions coming in so fast. It's hard to polish them. Let's see. User activated motion sensors. Yes. Do you like them? I do. In the applications that I've used them in, I find them to be really helpful, provided they're installed correctly. And I like them for things that are really, like we have, there's examples of permanent exhibits. We have some things that are on permanent exhibits. They're especially helpful for that, because they're not, the object isn't receiving light constantly. It's only getting light cast upon it when there's a visitor present looking at the item. So I like it for that reason. Is someone, there is the, was it, what was the question exactly? Someone just suggested that as an option and then actually someone else commented that, Yes, it is. That they're finding the activation not really accurate. And I suppose just like anything else, you know, you have to try it for your circumstance. Yeah, it has to be set up correctly and it has to be sensitive enough. I think there may be ways of adjusting the sensitivity. So depending on how close one needs to get to actually activate the light, that might need to be adjusted if it's not working. Right. We had a great question from Sunny Hawaii where they have a wonderful wall full of windows, which I would want if I were in Hawaii. But I have, and this is, I know a pretty elaborate question and it's very elaborate for those who are in historic structures. But to put correct filtering on windows, it's probably a job for a professional. That's the question. I would recommend that simply because applying films to glass can be tricky. So if, especially if you're talking about windows in an historic structure, you're worried about appearance, that sort of thing. Plus they're going to have a wider variety of films to choose from oftentimes. I found when I have done this before, working with these kinds of companies where there have applied films to some of our exhibit cases that are in less than ideal spaces in terms of light. So they can give you different ranges of darkness. So you can have it filter out more light or less light depending upon how much light is coming into the space. You can also, you can also, if you have the windows, you can have the windows filtered, filtered, excuse me, for one level. And if you have things that are really light sensitive, you can always have a drape or something that's placed over the object. If it's like a framed object or something, you can put like a, sometimes places put like velvet sort of drapes over things and the people who are visiting can lift it so they can see the object. So that's one way to protect them as well. Right, right. Yeah, that's a nice option too. Yeah. Especially in historic, I've seen that done, especially in historic homes that have paper or works on paper on display in cabinets. Right. And that's ideal. And pretty cost effective I'd say too. Yep. I just want to give you a couple more. I don't want to get us behind because you've got a whole other sections to go. Yeah. We had someone say, a textile conservator mentioned that using a window screen in a fluorescent is a helpful way to reduce UV. And I know there's lots of interest in low cost solutions. Yeah. Window screens. I don't see how that would reduce ultraviolet light. I could see how it might reduce visible light because depending on the size of the screen, like basically how tightly woven the screen is. Oh, you know what she's thinking of? There is a, I can't remember the name of it, but it's some sort of florist greenhouse type of material that people use in skylights that do reduce ultraviolet light. But it has something to do with florists or greenhouses or something like that. I don't remember what it actually is, but it does look like screens. It looks like a screening material. Maybe that's what they meant. Right, right. That actually is something. But in screen by itself might reduce visible light, but that's about it. It wouldn't, I don't think it would, I can't see how that would reduce UV. Yeah. Well, we can look into that. Yeah. I can find out. I can find out about that. Okay. Well, I see a lot of comments going back and forth like the group talking about them themselves, which is great. I think we got to basically, got to a lot of the questions. I'll scan it later and we'll make sure they get answered by hook or by crook, but I will turn it over to you to get on with humidity. Okay, cool. Thanks. So, thank you. So, relative humidity and temperature. So, I'll see if it works. No, it still doesn't click. Next, please. So, what is relative humidity? So, I'll start by mentioning, talk about water. So, water can exist in our universe as a solid, which is ice, a liquid, liquid water, or as a gas such as vapor. Next. So, absolute humidity, which is just general humidity when you say the term humidity. That's what you are talking about. That's the amount of water vapor that's in a given volume of air. And now that's nice to know, but it's not helpful to us because since the amount of water in the air will depend upon the temperature, we'd rather know that. Next. Relative humidity is the amount of water vapor in a given volume of air relative to the temperature of the air. So, that's the difference between absolute humidity and relative humidity. The relative basically means that it's relative to the temperature of the air. Meanwhile, absolute humidity is just the amount of water vapor in a given volume of air regardless of the temperature. Next. Next. So, what is dew point? Dew point is the maximum amount of water that can be held in the air at a given temperature. So, that's basic. So, and then that's called dew point. It's also called the saturation point. So, at that point, moisture will condense out of the air. And I found this really great video from a meteorologist in Milwaukee named Vince who actually does a very good job explaining relative humidity. So, I'm going to let the man with the little hat on tell you all about it. A lot more than 50% of this. Except it's darted. There we go. Hey everybody, Vince Cadella from Fox 6 with our video weather notes. Can you see or feel the moisture that's in the air? We can easily see it. Anytime you have a cold glass of water, let's say on a very warm air, chill the air, drop the temperature down to the dew point and then the moisture that's in the air condenses out onto the side of the glass. And there's the concept, dew point. So many people are confused. They like relative humidity because they've always heard that concept but they don't understand dew point. Here's one way to think about it. It's what the temperature that we need to cool the air down to in order for water to condense. So, if I can drop this air temperature on the side of this glass down to our dew point, any moisture, invisible moisture, water vapor that's in the air, we can make visible and condense it out. Here's another way to think about relative humidity. It's relative to the actual air temperature. So consider these two boxes. They're very different in size. This would be representative of very warm air. It can hold a lot of moisture. It has the capacity to hold a lot of moisture. This is representative of cold air. It can't hold as much moisture as warm air can. Well, relative humidity is relative to the actual air temperature. So, let's say if the relative humidity is 50%, well, that means that half of the air is filled with its capacity for water vapor. Well, 50% of this is a lot more than 50% of this. So a 50% relative humidity on a warm day is a lot more moisture in the cool day. So again, relative humidity is relative to the air temperature and it differs depending on the actual temperature of the air. The better measure is dew point. And by the way, dew point is a great measure for comfort. Dew points below 60 degrees, pretty comfortable for all of us. Dew points above 70, getting very sticky and uncomfortable for most of us as well. So it's sort of a mindset, a change in definition. Dew point much more representative of the moisture that's in the air. Hopefully that cleared some questions up. I thought that I really wanted to be able to demonstrate the box example. It's a really great way of sort of demonstrating volume of air and that I can't do this in tech land. So I was very grateful to Vince and his video so he was able to demonstrate that. So I'll talk a little bit about different ways you can measure relative humidity. Actually, a hair hygrometer. The human hair is actually the gold standard for measuring relative humidity as people probably know because this woman is demonstrating by her frizzy hair. And it was developed back in the 18th century. So we've been using it a very long time and it works quite well. Next, indicating cards. So how these work, you've probably seen a number of these in places. They contain salt solutions that change color at different relative humidities. So the way you would read this particular card is you would read between the pink and the blue. So where it's kind of almost pink, almost blue is in this particular card that you're looking at now. It would be probably close to the 20% range which is pretty dry. So the card's been hanging out in a dry place, apparently. Next. So a way to measure relative humidity and temperature is a psychrometer. The one I have pictured here is called a sling psychrometer. There's also one called aspirating psychrometers which are battery operated. You just wind it up and sit it on the table. But the sling psychrometer is so much more entertaining because you get to stand there and swing it around. And a grade school kid does a really great demonstration of it. So another video. Sorry, he doesn't have a hat, but he's a cute kid. So enjoy. Hi, my name is Shankar. And today I'll be showing you how to find relative humidity using a sling psychrometer. Now you see that on one side of the sling psychrometer there's a wet bulb. This will be the wet bulb because there's a little socket right there. And on the dry side there's just a regular bulb. So the first thing you do is you dip it in the water and then you sling it for about one minute like this. So about one minute has passed and our wet bulb is 16 degrees Celsius and the dry bulb is about 22 degrees Celsius. Make sure you measure it in Celsius which is on this side and not in Fahrenheit. So when you have them on degrees go to page 12 of your Earth Science reference tables and you see that the dry bulb is 22 so go down to 22 over here on the relative humidity chart and since the wet bulb was 16 it has a difference of six. So six and you have to pretty much move it over and you see that it's 53%. So the relative humidity using the relative humidity chart and 22 degree dry bulb and 16 degree wet bulb would be 53%. So that's it. Thank you. Great. So another way to measure relative humidity and temperature you've probably seen these in a variety of institutions is recording hygrothermographs. So it records data which is temperature and relative humidity over time to show trends on a piece of paper that is, you can see there, on the roll and you can usually do them either weekly or monthly depending upon how long you want to have the hygrothermograph running. Next, but the most efficient way to measure temperature and relative humidity these days are data loggers. So it's an electronic way of gathering temperature and range information but it does require computer software to interpret and graph data. What I'm showing on the right-hand side is the preservation environmental monitor version two from the Image Permanence Institute. They are one of the leaders in creating tools for environmental monitoring and interpretation. I saw early on that people were talking about eClimate Notebook which is an excellent tool for interpreting temperature and relative humidity data. I highly recommend it if you don't have it. There is a free version that you can use. We use it here at Yale and we use it for all of our libraries and it's very helpful. So I do highly recommend it. Next, so recommended levels. One of the things I really want to stress is the lack of fluctuation within a range is the most important factor rather than an exact temperature or relative humidity level. I think in years past people have been sort of stuck on the temperature needs to be this amount all the time and the relative humidity needs to be this amount all the time. That really isn't the case. Research is finding that with temperature of course lower is better provided that you can keep your relative humidity steady but keeping it within a range is perfectly acceptable and same with relative humidity. So when I say set points for relative humidity I'm giving a range of 30% to 55%. You can do plus or minus 5% if you have that kind of control but if you have gradual changes through the seasons that's expected and that's totally normal and it's okay. Most materials can handle that sort of thing especially when it comes to libraries and archives. We're really lucky in the fact that a lot of what we have is paper based and it's hygroscopic material meaning that it can readily absorb and desorb water very easily and usually without any sort of damage. So that's why we can do that sort of range. Some things like veneered woods a lot of different composite objects things like that you may want to consider tighter environmental controls but it really will depend on your objects. And for temperature set points we usually like to say no higher than 70 degrees if possible. Obviously lower is better the lower you can make your temperature the slower chemical reactions will happen. So that's why a lot of we recommend for a lot of different things cold storage being ideal for a lot of different materials like plastics, film negatives that sort of thing some textiles it's a good idea and someone did ask about whether or not rubber cold storage yes that would absolutely slow down any degradation that would be happening with rubber based materials so that is a good choice. So like I said you really want to think about a range and what your building can take, what your collections are and work within there rather than looking for an exact temperature and an exact relative humidity. At the end of the program there's a list the website that you can go to there's a variety of free webinars that the Image Permanence Institute will be giving about collection environments I highly highly recommend taking them if you're interested in learning more about your collections environment they will be really helpful to you. Next. A little bit about this yesterday but how does the environment affect your collections? So there's three types of effects with environmental influences physical, chemical and biological. Next. So some physical things that can happen with extreme changes in temperature and relative humidity constantly often I mean I'm not talking about gradual changes like I was talking about with the range you can have things that will change size and shape as I mentioned all organic materials will absorb water when RH increases and shrink when RH declines starting on the outside of the material and working toward the inside so what I've shown here is cracking emulsions on a photograph for some things if you have a lot of temperature and relative humidity changes that are happening quickly and often you can have materials that will end up cracking especially if it's a composite material like a photograph and the item on the right is a sprung vellum binding so if it gets too dry in a space your vellum can start to pull like the binding can start to pull away and then the binding needs to be re-humidified in order to actually get the binding to relax and close again otherwise there really isn't much that can be done with that it actually needs treatment so I'm going to go back down without tearing the binding unfortunately and that was caused as I mentioned by a drastic drop in relative humidity in this particular instance with the binding next so some chemical examples so temperature increases speed up chemical reactions that can cause acidic degradation so a familiar rule of thumb that people like to use and I'm sure Donya mentioned this is that chemical reactions double with each 18 degrees in Fahrenheit or 10 degrees Celsius increase with paper artificial aging tests indicate that 9 degrees Fahrenheit increase nearly doubles the rate of deterioration even in the absence of light pollutants or other factors and relative humidity provides moisture to fuel the reaction so the higher the relative humidity the more quickly deterioration proceeds and some other chemical effects that you see that I'm showing here corrosion due to acid rain so sulfur dioxide in the air ends up being a correct component of acid rain which is what happened to this particular statue and the item on the right silver mirroring on photographs it's a chemical reaction that involves moisture high relative humidity that actually chemically changes the silver component of the emulsion of the photographic element of the photograph it changes it back to elemental silver which is why it has that shiny appearance when you have a photograph it's actually a different chemical composition when it's actually formed and then if you add moisture to it it ends up going back to shiny silver which is why that dude's hair looks like it's silver and shiny next biological and this is mostly mold which I'll be talking about next week extensively so the example on the left is mold that was found on some Sanford maps and the item on the right is starch cloth a starch book cloth that was eaten by insects insects really like high temperatures and high relative humidity so high relative humidity so the higher your relative humidity the better it will attract pests like insects so controlling relative humidity and temperature so some things like to talk about lower cost or no cost ways to improve conditions so keeping your winter heat low that's really important in that when your heating bills won't be so high but also when we overheat our buildings we can really tend to dry out spaces and that's really bad for collections like 30% RH keeping your winter heat low temperature and relative humidity have an inverse relationship so when you raise the temperature your relative humidity is going to go down when you lower your temperature your relative humidity is going to go up so keeping your winter heat lower than you normally would means that your relative humidity isn't going to drop drastically so that's really important and the same goes for summer temperatures if you can keep your summer temperatures a little bit higher you're going to keep your spaces a little bit dyer and I'm talking about spaces where you really don't have a lot of relative humidity control if you don't have a method you don't have a way of controlling your relative humidity this is a way to do some to help somewhat someone asked about dehumidifiers they are an excellent way of controlling high relative humidity in spaces where you want to make sure that it is the right size for your space and will remove the right amount of moisture from the air so I included some links on the website for connecting to collections so that will help with choosing the right type of the right type of dehumidifier for your space needs and evening setbacks are okay the image permanence institute is actually doing some experiments now with the libraries and archives where we're actually shutting down our HBAC systems to see how that affects the overall preservation index of paper based materials and so far it's been working very well we've been turning off our heating ventilation and air conditioning systems all times of the year at night time and we're finding that the temperature and relative humidity shifts are really minimal so that's a really good thing because I know we've been talking about it for years and years that you need to keep your temperature and keep your temperature at the same temperature all the time not necessarily so keep your eyes peeled for that and that's stuff that you can learn from the free webinars from the image permanence institute ceiling windows yeah ceiling windows is important if you can make sure that you have not getting around your windows if you need to seal them up with plastic in some cases that's important to keep cold air out and hot air out in the summer and cold air out in the winter keeping outside doors and windows closed I know it seems like common sense but it's sometimes you just say these sorts of things blocking radiant heat from radiators if you can build sort of like wooden blocks that will keep the radiant heat from like actually being up against collections too and separate collections that need special conditions if we go to the next slide I'll sort of talk about that please micro climates, micro climates there are certain collections if you have things that are composite objects that are sensitive it's really important to store them in a way so that they are buffered from the environment that can be something as simple as an object being wrapped in a far flat paper housing inside a box which is inside another box that sort of thing the more layers of protection you have in terms of housing from your outside environment is really going to make a difference in how it actually affects your object remember I mentioned that temperature and relative humidity relative humidity especially affects an object from the from the outside in so if it's going to be coming at your object and it has to go through a box and a folder and a four flap housing it will take a far longer period of time for that relative humidity change to affect your object so housings are really really important also things like exhibit cases storage areas shipping containers, framing packages all of these that can be considered micro climates so here's some more information about micro climates and how to create them next so buffers for relative humidity control they act as to maintain a specific range of relative humidity absorbing and releasing humidity to maintain an equilibrium especially essentially excuse me next so some ways you can do that, silica gel it's a glass based product and the type that I'm showing here it has an indicator that changes color when it needs to be refreshed you don't want to use ones that have indicators that are made of cobalt which is blue because cobalt is a toxic metal so best to stay with silica gel or sorbid orange which is what I'm showing here or pro sorb and for our closed case or container about 20 kilograms per cubic meter for one year is sufficient to keep a relative humidity of 40 to 50 percent stable next saturated oh did I take one out oh I check what slide out by accident excuse me there is something called saturated salts but that's not something I would recommend anyone using simply because it has problems with rusting metal and things like that so please ignore the second bullet there but the third one is important which is something I was mentioning earlier which is buffering with layers so if every layer you have above your object will protect it so what I'm showing here is a framing package and all the different levels that protect your object from both sides will protect it from the outside environment so and keep in mind that only acid free materials should be touching the object itself as it shows in this framing package image and the more materials in the package the better protected it is from the outside environment next okay we are at pollutant so we can pause again and I can answer some of your questions that are buzzily coming up on the left side here thanks so much Tara we've got about 20 minutes so do you want to keep an eye on time I put in a couple more light related questions but maybe we can answer those at the end if we have time I wanted to get into more on rh so you've seen some questions here do you want me to read them out loud yeah let me see because I can't quite move the parking lot okay so Robert wanted to know how effective is a desiccant wheel technology in reducing rh levels in southern climates are you familiar with any studies or white papers done on it desiccant wheel is a really good way of reducing relative humidity what I would recommend for things like that is a desiccant wheel would only be really effective in a purpose built building simply because you're going to have a good barrier and good insulation a lot of older homes things like that what would end up happening is you're trying to dry out the outside and also might end up causing other problems to the historic structure but for a purpose built building those are excellent we use that for our high density storage facility and it maintains 35% relative humidity year round flat line great and what's the best equipment to automatically balance for fluctuations in humidity I think you've just hit on that at the end I mean microclimates is one way to solve it yeah balance the fluctuations in humidity maintain the desired level if you're talking about high levels of humidity a dehumidifier probably is if you're talking about equipment it kind of depends upon the problems you're having if you're having low relative humidity you might need a humidifier during certain times of the year because I see they're in New York if it's high relative humidity a dehumidifier it can be helpful also protecting your objects if you have no way of actually using electronic equipment like that it's best to try to do really good housings for things but usually I recommend supplemental things like dehumidifiers and humidifiers if need be and so you did put a resource up on the web page about how you determine what size dehumidifier you need for the space so we had a question from Mark in Missouri so anything more to add on that besides checking our site for those sources those are two really good sources and they have really good ways to make it practical for you to figure it out so no I totally look at those those are very helpful we had a question from Alaska yesterday I mean low humidity is a challenge there and so you definitely say use humidifiers is there a variety of what's available out there is there something that's more high quality for a collections environment well in terms of how the humidity is delivered it can vary there's ones that are sort of aspirating water humidifiers there's evaporative humidifiers there's different types of things that really kind of depends upon well if you want to be energy efficient how big your space is how dry it is there's a lot of different factors there is I actually don't have because usually where I am it's high relative humidity not low so I've been focusing a lot on that but maybe I can take a look and see if there's a source on a good way to choose a humidifier okay so I can write that down here and everyone has been saying some people nailed it it's shade cloth that is the stuff from the greenhouses that you should use for blocking UV okay good we'll see again we'll see if we can find some more information about that and post something on the site we you just mentioned desiccant light can you just explain that a little bit more oh desiccant wheel sure what a desiccant wheel is literally it's a giant wheel full of type of material that would be drying so it can be something like silica gel that sort of thing so what it does is it rotates through the air stream and adds dry air into a space and it automatically refreshes itself it's kind of cool by rotating over I think at the heated element and then it dries out the desiccant that's in the wheel and then so it's usable again so it's something that's like almost an ongoing resource that can be used for a really long time it's really nice and it's very expensive but it really does the trick if you have a purpose built space and you need to keep it at a constant relative humidity it's a rockin' thing okay cool um Claudia had a question let's say from Texas she said our area often has very dry outside air is there a minimum humidity level we need to aim for I try to aim for 30% usually 30 to 55 is the range where I usually give people you go about 55 and keep going up you worry about mold and you go below 30 you start to worry about drying things out um and also especially if you have volume in your collection it's really important to keep the relative humidity up higher but if it's mostly paper you might be able to get away with 25 but I would usually say 30 okay I'm going to let you go on we did some questions about the silver mirroring a little bit and there are a couple other questions that started to talk about pollutants so I think you might answer them in this next section and then we'll see what we can clear up at the end okay thanks okay pollutants next slide please so there's a couple types with airborne and gaseous pollutants there's particulate and some sources that we get from particulates are mostly from industrial pollution pollutant smoke from cars smokestacks, clothing fibers dead skin cells that's what's mostly in dust like your regular household dust cigarette smoke and the picture I have there is a microscopic shot of dust so you can kind of see all the different components that you'll find in it so generally they're kind of city tarry they may have acidic components that can cause metallic corrosion and dust also attracts moisture next the measurements and standards are denoted in microns so larger than 15 to 20 microns will settle smaller ones will float around until they're caught in something and quantity is measured usually in micrograms per cubic meter so and now there is nowhere in Europe or North America where background levels of particulates are lower than 20 micrograms per cubic meter hooray industry next so control, multi-stage filtration is usually a really good way to control dust and other sort of airborne allergens that would be particulate so what you want to look for in terms of your filtration levels is the minimum efficiency reporting valve or the MERV value so the higher the number the more the filter can filter out you just have to make sure that your air handling system can handle higher levels of filtration otherwise you're going to block airflow so I've actually added a link to a chart that gives you all the different MERV filtration rating systems so it'll give you an idea of how much it will actually filter out but the more you can filter out the better you'll be for your collection in terms of reducing the amount of dust and other sort of harmful airborne particulates next gaseous pollutants so here's some that that you can that you will find in most common industrial areas sulfur dioxide and water equals sulfuric acid which is a primary component of acid rain nitrous oxide and water and nitric acid again another sort of acidic rain component as well ozone and that's actually a component that's found in smog and that's why tires break down much more quickly in Los Angeles than anywhere else in the world ozone breaks down the rubber really quickly from the smog so there's also from aldehyde, acetic acid, and chloride those are things that are usually found as internal pollutants they'll be found in wood components inferior plastics that sort of thing so you're going to find those final three mostly from interior pollutants next the gaseous pollutants as I mentioned external sources are going to be primarily the burning of fossil fuels and they're going to be the heaviest in the most industrial parts of the world so below the picture the lower picture is a picture of smog and Beijing so that's a good example of a highly industrial area next and as I mentioned from aldehyde, acetic acid, and chloride they're mostly going to be from internal pollutants so HVACs air handlers without proper filtering inappropriate building and storage materials certain types of wood there's these things called electrostatic precipitators which are a form of a way of still trading out components in older air handling systems and they produce ozone so you can use those and chloride from poor housing materials especially poor quality plastics next so units for unit of measurement pollutants are usually measured in micrograms per cubic meter and gasses are often measured in parts per million or parts per billion by volume so there are different ways you can measure them paper and textiles, badge monitors and corrosion coupons like that image I'm showing there that's a particularly analytical way of doing it, you put it in that particular box in a room it will take it will measure the amount of gasses pollutants in the air and then you can send it back to a laboratory and it can give you results it's usually quite expensive so next if you want to do it on the cheap you can cut pieces of silver and copper, I don't recommend cutting lead as it is in this example but you can use silver and copper and just sort of set them out and keep a control in your desk in an envelope and leave them out and see if you have any corrosion products if silver starts to tarnish you've got sulfur hanging around and if copper starts to turn green you've got chloride problems so it's one way of at least doing a quick and dirty way of checking if you actually have any pollutant problems next this is just a slide to give you some ideas of standards for pollutant levels and since you'll be getting a copy of the presentation afterwards I'll let you all peruse that next so methods of control, limited exposure obviously, so pollutant level indoors are about half what they are on outside levels so keep outside air out and inside air in you do have to let in some air with air handling systems I think the standard usually is 20% but as long as you have good filtration that's why good filtration is so important to keep the outside air as clean as possible next you can also do internal filtration ways there's ways to filter it out water spray is one activated carbon is another activated carbon is probably the easiest one because it's just a dry filter that you stick into your system so most units nowadays like I say have activated carbon or zeolite dry scrubbing filtering so you can either have your system be self-contained for single room use like the one I'm showing here or you can have one as an easter that can be put onto your system so if there's you have particular sensitive objects if you have a room full of silver and you're in a high industrial area you might really want to invest in gaseous pollutant filtration so things don't tarnish really quickly next a company called Corrosion Intercept makes this little tiny system that you can put this device inside a small area and it will filter out gaseous pollutants so you can put it in a small case like in an exhibit and it's available through a vendor called University Products and that is available next so damage from pollutants I'll show you a really common view of the item on the right y'all know it's the Statue of Liberty so when we put up the Miss Liberty she's made of copper so she used to look like copper and now thanks to all the pollution that she has endured over the years she is now in a shade of green so she has turned from copper to copper sulfate thanks to oxidation and acid rain and also what pollutants can do in terms of acid rain and other things like that is it can erode pieces of calcium based like plaster that sort of thing like I'm showing here this poor statue has lost her face and the detail in her dress so that's pretty common in industrial areas next so damage from pollutants this is a close up image of red rotted leather so pollutants can cause yelling of paper sulfur damage to photographs and sulfuric acid also can cause is one of the components that causes red rot in vegetable tanned leather which is what you're seeing here so that actually is mostly due to pollutants in the air more than anything else rather than I mean relative humidity does help speed up that reaction but it's actually mostly due to pollutants okay next that should be the end that is the end and I want to make sure before the time is up today I want to put up again the link to our homework which is a survey monkey and it's also linked to on this collection of care basics web page and I want to get to some questions just regarding just we can try to go back and get some others but with the what Kathy wanted to know with doors and windows sealed how do you get rid of pollutants so if you're really making an effort to control temperature and humidity and then you really closely seal things up do you have any advice there I'm sorry could you internal pollutants if you're really conscientious about keeping external temperature and relative humidity fluctuations from affecting your space she was worried about the internal pollutants that might be trapped inside okay yes usually we're more worried about it when we're talking about new products so if you've just installed carpet for example that would be an internal pollutant we're not talking about things that have been in the space for a really long time so this is usually new building materials that sort of thing is our biggest concern so I think if you're sealing everything up I think that's probably more important to keep the outside stuff out especially dust that's a real problem with questions so yeah and then see Janine said she has airborne pollutants when air is blowing in through the windows and doors and I guess that's the same the same sort of thing that's sealing would be helping that sort of thing yeah and how would those silver and copper coupons how long would you leave those out you can leave them out I'm trying to remember how long they left them out when they did the testing here I'd probably say like a couple weeks it doesn't have to be for very long if you have it maybe a month tops and I know we went through all of this very quickly especially at the end but you know people have a schedule so I did share your email address in case there are questions that didn't get answered and we can also put those up if you've attended with a colleague or a friend let us know in this chat box I've just dragged into the screen we want to make sure that if you've attended by yourself don't worry we know who you are because we saw your login but if you have someone else and you want to make sure they get credit for attendance please tell us who the other person was let's see if there's other questions we can get to how would you determine the amount of silica gel to use I think I gave for I think it was 20 what was it I did give that where are you sorry I'm paging backwards into where I said it I just have to find it again I want to say 20 kilograms 20 kilograms per cubic meter for one year is a pretty good rule of thumb and Donia also mentioned on the chat that there's a calculator online that she will find the link for and we can get that up too okay cool a couple of questions came in just wanted to let the audience know came in on about storage materials and how do you check for acid those are great questions and Donia is going to totally answer them next Tuesday when she talks about storage because you got into microclimates which is great so a lot of these issues with pollution with fluctuations in relative humidity and temperature can be combated with good storage and so then a lot of those answers will be coming to you next Tuesday so are you able to answer this question about silver mirroring problems and what can be done with them we're going to have an entire web course coming in May from actually one of the best photo preservation experts in the US we're very fortunate to have her teach this class so I know that will be addressed fully but just to keep people give them an answer before May you have any other basically it requires a photo conservator to do treatment that involves changing the chemical composition of the silver so it's using and I don't remember I think it's some sort of reducing solution so it's actually it's complicated yeah it's it's chemistry and we're just at 3.30 I see those other questions about light do you see reflecting light reduce it's cut off on my screen unfortunately I can only see part of it is that better I see reflect ah thank you why does reflecting light reduce damage does UV reflect more or less than visible light what happens when you reflect light is that the surface that it reflects upon is actually absorbing some of the energy that's coming from that light source so the reflecting light actually ends up being less energy so if you're actually reflecting it off something that's a darker color like black something like that that's going to absorb more light it's actually going to reduce the energy that's reflected off so it's light physics that's essentially why so UV um UV it doesn't necessarily reflect more or less than visible light it's kind of the same sort of thing it's still something that can be absorbed or absorbed into the surface that is being reflected and would there be any benefit to stagger the cycle of replacing the bulb since they have a finite lifespan I'm not sure I understand that question but this last one in the formula intensity times time when is real damage occurring there's actually a link that I've placed online to the light that to the Canadian Conservation Institute which is the light damage ruler so it actually can show you how different colorants are affected by light damage over time and you can put in different components such as what kind of light is being exposed to whether that be daylight or an incandescent bulb or a UV bulb that sort of thing you can actually see it in real time and see it in action and I can't forget what would there be any effect to stagger the cycle I guess like yeah I just wondered if in terms of maybe cost effectiveness some of these newer light bulbs are so expensive I'm not sure if I understand it either but Nicole if you can send us an email with more information or put it into the chat now we can find you an answer so there's some really great conversation happening in the chat and we will focus our welcome to stick around and keep those going for a few minutes I'm happy to do that but I know others need to get on to the rest of their day so I just want to thank everybody for attending and thank Tara for her help she's going to come back and talk about mold which I know is going to be very important and interesting and that's next Thursday I believe so we will see you then and thank you for your help and thanks for everyone who came and joined us today stick around and chat and definitely keep an eye on the web page the links we talked about today thank you very much thank you