 Who's to you? Your host? Susan Berger from the FAIC. Go ahead, Susan. Hi, everyone. Happy New Year. We're happy to have you here, and this is going to be a nice way to start the new year. I'll just go through my slides here really quickly. If you're not a member of the CQCC Announce List, that's probably the best way to get announcements from us. You can go to this website and sign up. And usually that's only one or two announcements a month. I also post on Facebook and Twitter upcoming events, so that's another way. You can also join our new discussion group community because we no longer have a form on the website. It's now within the FAIC, so you can go to our website connecting to collections.org, and it will give you instructions on how to join that. And you can always contact me. This is my email address. I'm happy to hear from you if there are problems or good things or whatever. Yeah, just feel free to contact me. We have two courses coming up. In February, we have one on collections management with John Simmons. In March, April, May, and June, we have the first Reorg project course being offered in the U.S., so take advantage of those. Registration is open for both of us right now. And the webinars that are coming up, we have one in February on copyright, one in March on emergency planning for gardens and living plant collections, one on old loans in April and one on caring for herbaria. And that's what's coming up. Check the website as soon as I have everything. I post them. And, well, you folks in Las Cruces are lucky where it's sunny. I'm a Santa Fe word to not. Okay, I'm going to turn this over to Rachel, and we'll go. Good afternoon, everyone. Hi, I'm Rachel Irons-Dyne. I am a conservator in private practice in the New York area. And I am very pleased to be able to talk to you today about silica gel. Sorry, how? Let's make sure I'm advancing the presentation here. The arrows in the lower line. You just did it. Okay, sorry. We're jumping ahead. Okay, sorry. Well, I was serving as a member of the Connecting to Collections Care Professional Development Working Group. I volunteered to present this topic as I was spending a lot of time working with my museum clients, correcting misunderstandings about silica gel and how it can be effectively used. For those of you who already have a sense of collection care basics, I hope that you'll stick with me while I first review some introductory material and deterioration and environmental control. This foundation is important in understanding our environmental needs and whether they can be fulfilled by using silica gel in a microclimate. Then we'll really get into the nitty-gritty of silica gel types and formats and how to use it properly in common museum applications. I hope after this presentation, even if you feel that using some of the equations isn't your thing, that you'll be able to ask good questions of a preservation vendor and choosing a gel for your particular application. Susan, can we just put up the first poll to get a sense of how people are using silica gel if they are? Okay. Well, that's interesting. So it seems that most of our audience is not using silica gel at the moment, but I'm hoping then I will have a lot of useful information for you. So let's start with a little bit of a review. Our goal is collection care and preservation professionals is to extend the life of the material in our care. I find the way that the Image Permanence Institute discusses deterioration to be useful in understanding what we're concerned about. IPI uses three broad categories. They talk about chemical deterioration, mechanical, and biological. So chemical really refers to the reactions occurring within the object, how they age. Mechanical refers to the kind of physical damage such as cracking, warping, delamination, slumping, and biological damage means mold, fungi, or insects and vertebit pests. We often speak about the agents of deterioration, which are defined as primary threats to our collections. And probably the best description of these 10 general categories is available on the Canadian Conservation Institute's website. The job is to determine how we can detect, block, report, and treat the damage these agents cause. So today we're going to focus on one of the environmental agents, incorrect relative humidity or RH, as it's a major factor in all three forms of deterioration that we just discussed. PCI breaks down incorrect RH in four ways. First is, RH is too high. High relative humidity is responsible for corrosion of metals, mold growth, and mechanical damage of hygroscopic organic artifacts. High relative humidity is generally considered 65% and above. Mold germinates at around 70%, and so most guidelines for the upper RH limits pop out around 60% RH. Next would be RH that's too low. Organic materials will lose moisture to the ambient environment if the RH is too low. Generally 30% is considered the lower limit. Below that, artifacts may shrink, becoming desiccated and embrittled. Next we have fluctuations in relative humidity. This has been, for many institutions, the most problematic issue in environmental control. When RH fluctuates, the moisture content of the artifact will fluctuate as the PCI equilibrium with its environment. This results in expansion and contraction. For artifacts made of multiple materials that react differently to changes in RH, or artifacts that are constrained or under tension, such as stretched skin for Native American drums, the different rates of equilibrium can cause cracking splits and other forms of damage. And then we also have a fourth category where the RH is above or below an object-specific critical value. There are some types of artifacts that have specific environmental needs based on their materials, composition, or conditions. For instance, archaeological metals benefit from low relative humidity, while unstable glass requires moderate 40% to 60% RH. So sometimes our goal is to prevent extreme, and other times our goal is to provide a specific set of conditions. And we know that we often have trouble in doing this. The Heritage Health Index report published in 2005, which was the first comprehensive survey to assess the condition and preservation needs of U.S. collections, found that many institutions have problems in creating appropriate environments for the long-term preservation of our nation's cultural heritage. A quarter of institutions reported no environmental control for their collections, and clearly even ones that did have seen damage. So you guys on this call are not alone if you're grappling with these issues. The Heritage Health Index report resulted in a number of initiatives, among them the collection Connecting to Collections Care Platform we're on now, aimed at providing information to address preservation issues. And along with that, we've also seen a real shift over the past decade in recognizing that some of what people thought they needed to do, like providing strict environmental control at 70 degrees Fahrenheit and 50% RH, plus or minus 5%, may not only be unachievable for some institutions, it may be unsustainable for most and unnecessary for many. So that brings us to our topic at hand. We know that we want to control RH, but we recognize that for most of C2C care core audience, controlling the entire building environment may be impossible. It may be easier to control one specific space, like the storage room on the right here depicted in one of CCI's case studies. But if recent research is showing that many collections can withstand a broader range of RH conditions than we previously thought, it might be most efficient to focus on controlling the environment for our most valuable, important or sensitive items, like you see here on the left. And the way we can do this is by creating microclimates. For our purposes, whether in storage or on display, this can mean using a container, like on the left, a cabinet, or a vitrine, or some other form of containment to provide an environment for a select grouping of artifacts that's different from the surrounding ambient environment. Microclimates can be used to protect our collections from incorrect relative humidity, as well as a whole range of other agents of deterioration, such as pollutants, physical damage, light, water, dust, and more. But it's important to recognize that elements like a type seal on a cabinet in between that makes a microclimate good for controlling RH can also have adverse effects if pollutants are trapped inside. There are two ways of controlling microclimates. Active environmental control includes HVAC systems, and on a smaller scale, systems like those sold by Jerry Shiner of Keepsafe, or the new Zoomador Proton Exchange Unit that you're seeing in the second image from the left. These are using electronically powered mechanisms to change the environment inside the microclimate. In contrast, on the right, we have a couple of examples of passive control. You have a vitrine here and a storage bag. Neither of these need electricity. Instead, they rely on having some sort of hydrophilic buffering material that will create a reservoir to either absorb or give off moisture within the enclosure. The process works by diffusion, so it takes some time. In choosing between an active or passive system, you'll want to consider the humidity level and range desired in the microclimate and how different that is from the ambient conditions. The size of the enclosure, materials that it's made out of, and construction, as that will determine its leakage rate, meaning how fast the air inside and outside will be exchanged. You also need to think about how long you need the microclimate to work. Is this the short-term exhibit lasting three months, or basically a permanent display or storage solution? The size and composition of the collection items will determine how well they buffer themselves and become a factor. And, of course, there are practical considerations like cost, staffing, expertise that will all play into effect. Both types of systems require time for setup and maintenance. Generally, active systems require a lot of investment in the setup, but should be easy to maintain, whereas passive systems may be easier to set up, but need regular ongoing maintenance. Today, we're going to be focusing on passive control, but there are some other good webinars on the CPC care site that delve into appropriate environmental conditions, HVAC systems, and other active measures. In particular, you might want to check out Alice Carver Kubrick's webinar, Storage Environments, The Big Picture, and the webinar by MyBac and Conrad, when less is all you've got, budget-conscious solutions to protect collections on display and in storage. Okay. So, let's start getting into the fun stuff. There are multiple sorvents that can be used for passive environmental control, and they're used in all sorts of industries. You've undoubtedly seen those little packets with your new pair of shoes that they do not eat, and the packets in with electronics, pill bottles, or food that need to stay dry. Let's quickly review what some of these materials are before we focus in on silica gel. Susan, can we do poll number four now? I'm just interested in sort of seeing if you guys are using any of the other kinds of methods. Okay. Well, I think everybody's still in the right place. Most of you seem to not be using anything at the moment. Okay. So, what you're seeing here is sort of a range of, on the right we have a couple preservation suppliers, Gaylord, Archival, and University Products. Just as an example, and on the left, we have ULINE and some others that focus in on defecants. And so one of the questions that I sometimes get is, you know, why can't I get the cheaper stuff from ULINE? You know, why is there such a big markup, or why is this product more expensive? And we're going to get to that. So, the earliest attempt to control the environment in display cases appears to date to the 1930s, where a British patent was awarded to a specialty design museum case with built-in trays to hold salt solutions. Different salts when made into a slushy saturated solution will maintain a specific RH in a contained environment. So, for instance, at room temperature around 20 degrees Celsius or 68 degrees Fahrenheit, lithium chloride will hold at 11 percent RH, magnesium chloride at 33 percent, and sodium chloride at 75. You can easily find tables of these measurements online. This is a low-tech method for buffering an environment, but over time the salts can creep over the sides of the containers and make a mess. Plus, conservators are generally leery of adding salt in proximity to our collections. That's why we stay away from defecant salts like these calcium chloride bags sold by vendors like ULINE. But we still use this technique in some circumstances, mostly to create environments for checking calibration of equipment like data loggers, as you see here on the right. Here you're seeing an outer Tupperware box and then an inner box where part of the lid has been cut away and there's a membrane to contain the salts. But inside that sort of breathable fabric is a saturated solution to allow us to check whether these data loggers are still within their calibration range. Another method is activated clays. Activated clays like marillanite and bentonite are naturally occurring minerals that you'll see sold. Because they aren't synthesized products, they're generally cheaper to buy. These clays are chemically inert and non-toxic, making them safe for use and disposal. The clays work well as a defecant with the ability to absorb around 25 percent of their weight in water without swelling, but they're not as good as the buffering material, so they can be less useful for some of our museum applications. They aren't as efficient as silica gel, so you may need to have space for more clay packs than you would need in silica. So ultimately, while it's an acceptable solution, it probably isn't an efficient use of your preservation funds. There are other sorbents like molecular sieve, zeolite, and activated alumina, but these are not commonly used for general museum applications, so they don't want to spend time on them today. But it's good to understand that there are other materials out there that work as sorbents, but you would have to have a very specific application to make their properties or their costs worthwhile. So that brings us to silica gel. But before I start talking about the details, I want to mention two important publications that form the best resources for this topic. They're also listed at the end of the presentation and in the accompanying handout, and they're available free online. The first is the Canadian Conservation Institute's 2018 update of technical bulletin 33, Silica Gel, Passive Control for Relative Humidity, by Jean Tittrow and Paul Begin. And the second is the 2002 paper Demystifying Silica Gel by Steve Weintraub of Art Preservation Services. I'll be pulling liberally from these two publications with the permission of the authors. Silica gel is a chemically inert, non-toxic material composed of amorphous silicone dioxide. It's a synthetic form of silica, and it's produced in either granular or beaded form. Beaded silica gel has a higher mechanical strength than granular form, so it generates less dust and is therefore our preferred method. Silica gel was patented in 1919 for use in adsorption of vapors and gasses and gas mask canisters during World War I. And by the 1970s, it was a common solution for controlling RH and museum displays. Silica gel beads have a vast network of internal pores, creating a lot of surface area. Weintraub describes that the surface area of one teaspoon of silica gel beads, approximately one gram, if spread out would be approximately the size of a football field. The gel is so successful as a desiccant because it adds fur's moisture into its pores, up to 40% of its weight in some cases. Silica gel comes in various forms. It's cheapest to buy as loose beads, but it's often more convenient to contain it in a cartridge or a sachet for ease of handling and use. The sachets are generally made from some sort of permeable fabric, like Tyvek or Wimei. Partridges should be designed to maximize surface area. The gel can also be made up into sheet form, but this is best used for specific applications like microclimates for painting rather than for general control. You'll also hear various product names, gel types, and grades mentioned. This can get confusing. Some of them would be rapid gel, prosorb, artsorb, regular density, or rd gel, high density, or hd gel, type A, B, and C. To understand what these terms mean and why they're important, you have to take a closer look at how silica gel works as a sorbitant. I'm going to skip ahead to this one. By using silica gel in a reasonably tight microclimate, we can smooth out the peaks and valleys of our ambient environment so that our collections don't feel such abrupt shift, either daily or seasonally. Most sorbents are used as desiccants. Think back to the example of the food and pharmaceuticals where we see those little packets used. In museums, we sometimes use silica gel as a desiccant to reduce RH, for instance, to store metals at a lower RH than other artifacts in storage. But we mostly use it as a buffering agent, and that has some important implications for how we select and use silica gel. Can we take a look at poll number two? So for the percentage of you that are using silica gel, I'm interested in seeing how you're using it. Okay, well that seems pretty typical that most are using to desiccate, but also to buffer. Now we're going to pack up for this one. So I briefly touched on this before, but organic materials are hygroscopic. They absorb and release water depending on the RH of the surrounding air. This process will continue until the interior moisture content of the artifact reaches equilibrium with its environment. This is called the equilibrium moisture content, or EMC. The Image Permanence Institute's research has demonstrated that moisture equilibrium, in contrast to thermal equilibrium, even temperature, the moisture equilibrium is relatively slow. Depending on the nature of the material, its size, and surface area, it could be days or weeks until an artifact equilibrates to a change in RH. Placing artifacts into a micro-environment, like a box or a cabinet, will slow this process even further. In wine treads chart on the left, you can see that silica gel, both the regular density and art source, reacts faster to changes in RH than the organic materials such as wood, paper, or wool. This means that the gel will buffer the environment in an enclosure faster than the artifact. This is really a surface area issue. The silica beads have more surface area than even a text block of a book. So generally, we don't want our collections to buffer themselves. So the capacity of different types of gel to buffer is affected by factors such as the capillary pore size or the inclusion of hygroscopic salts, resulting in a wide range of performance. Therefore, it's important to compare the buffering capacity of different types of silica gel to determine which silica has the best performance for a specific application. This variable has been known as the specific moisture reservoir, and it is described with the variable M. But M varies due to several factors, including the point along the EMC on relative humidity isotherm, at which it's measured. So think back to that graph that I showed you before. Two back here. So the point at which you're measuring it here, the magnitude of the RH range used to determine the M, whether it's measured along the adsorption or desorption isotherm, meaning whether RH is going up or whether it's going down, and hysteresis. So let's get our heads around hysteresis. When we measure the M value of a gel, the absorption adsorption curve as RH rises is not the same as the desorption curve as the RH goes back down. So you're not going up one line and coming back down the same line. As you see here, there's like a bit of a loop going on, and the loop isn't, you know, sort of linear. It flattens out in places. This creates a lag. And so this upper part of the curve in this RH range, that's what we're talking about when we talk about hysteresis. So to simplify, if we just want to use silica gel as a desiccant, then we can talk about the M value. But because we often want to use silica gel as a buffer, and if we are both adsorbing and desorbing, meaning we're taking in humidity and giving it off to buffer in our microclimate, then we need to take hysteresis issues into account. So instead of using the M value, we refer to MH, which is a better measure of the gel's buffering performance. MH is calculated by repeatedly cycling silica gel between adsorption and desorption within a specific RH range until a constant value is measured and hysteresis is taken into account. So MH reflects actual buffering performance, and ultimately the higher the MH, the better that gel buffers. The silica gel industry divides silica gel into three standard types based on the core size of the gel, A type, B type, and C type. A type silica gel has good moisture absorption capacity between 0 and 50% RH. Above 50% RH, the capacity to adsorb moisture diminishes. For this reason, type A gel is an effective humidity buffering material within the range of 0 to 55% RH when it's used in sufficient quantity. It is not recommended for humidity buffering applications above 60%. Type A is also sometimes called regular density, or RD gel. C type and C type have low moisture absorption capacities below 70% RH and are not appropriate for humidity buffering applications below 70%. This means we normally don't use these kinds of gels in museums, but you might find them in product-like kitty litter. High performance silica gel refers to special types of silica that have good humidity buffering characteristics between 0 and 70% RH. So, wrap-a-gel, art-sorb, and prosorb fall within this category. In the CCI technical bulletin, you can see their MH calculations for several types of sorbents. So what does this chart mean? Does it mean that wrap-a-gel, prosorb, and art-sorb are better gels? Because what you're seeing here is that in this first column, this MH, 50 plus or minus 10, with an RH around 50%, you see wrap-a-gel, prosorb, art-sorb, these high-density gels have the highest numbers. The next grouping are these RD type A gels, which are about 1.9, 1.1. And then below that, you have the zeolites and the activated clays. And you can see that at moderate humidities, they're not quite as good as a buffer. So this chart there doesn't mean that wrap-a-gel, prosorb, and art-sorb are better gels. It really depends on your application. For these three gels, the MH value is the highest in the mid-range and above in the third column over here. So these high-density gels will perform better than others if you're trying to buffer or maintain environments between 50 and 60% RH. If you need to buffer at a moderate RH, then it will be worth spending money on one of these products because they'll perform better. In the case of high-performance gels, wrap-a-gel and prosorb will perform similarly as they have a fairly linear M value through the normal range of museum environments. With art-sorb, you can see that its MH value falls off in the lower humidity range, seen here in the central column. Regular-density gel and the orange-indicating gel, which is also an RD gel with a colorant, have much lower MH values in the mid-to-upper RH range. But they perform as well or better at lower relative humidities. So if you're using your gel as a desiccant, you can save money by buying a regular-density type-a gel from SmallCorp or another preservation vendor, or the new art and gel from our preservation services, rather than spending the money on a high-performance gel. And you can see that the gels are all better buffers than the desiccant clay. But if you're looking to maintain a humidity below 40%, then an A-type gel is comparable to the high-performance gel. That is, the 45-50% RH range is really where you see the split between the RD and the HD gels. So you would need to compensate by using a lot more A-gel to get the equivalent amount of buffering at a high RH. So now let's take a break from some of these formulas. Well, I lied. We're not going to take a break quite yet. But we are going to sort of start to bring this around to less theoretical and more practical. The question of how much gel to use is one that I'm frequently asked by my institutional clients. The most accurate way to calculate the amount of gel is using this formula. But as you can imagine, it can quickly make you go cross-eyed. I use an Excel spreadsheet to help me with the math. Over the past number of years, various manufacturers and distributors have created online silica gel calculators, where they've put up quick and dirty guides for determining amounts. But these need to be handled with care. For instance, without picking on them, the TALIS website states, 1.5 tons of ArtSorb is recommended to maintain one cubic meter. And other sites make similar statements, even if their values change. But a simplistic guide like this doesn't take into account all sorts of important details. How leaky is your case or your cabinet? What is the ambient condition versus the condition you want to maintain? Do you know an accurate MH value for the gel you plan on using? How tight do you need your control to be? Is this a temporary exhibit or do you need to control conditions for a longer period? I'm not trying to duck the issue here. Some of the vendors present accurate MH values, but others don't. So the amount of gel you will need and how much that costs will primarily depend on the MH value. If you can't get that information from the vendor or they can't show you the testing that supports it, choose a different vendor or product. If you're at an institution that has a stock of unlabeled products, see if you can sort it out by type. Sometimes the packaging can give you some clues, and that can be helpful to figure out what you might want to use for what application. So there are a couple of mistakes that I see frequently in my work. One is simply not using enough gel for the volume of air in the retreat. On the right here you see a large case with four cassettes of gel at the bottom. There was absolutely no desiccating effect going on here for these sensitive maritime iron artifacts. The case on the left had a lot more gel for a much smaller volume of air and was doing a good job maintaining the desired environment. The other mistake that I see a lot is not taking into account the D value in the equation. Let's just quickly go back. The D is the difference between the RH outside the enclosure and the targeted RH inside. So if you're trying to change the environment rather than merely buffer it, if you have an ambient RH in your gallery of 45% and you want the case to be under 30% RH for your metals, you don't want to put in 30% gel. You would want to put in dry gel, meaning gel that is under 10% to pull the RH down far enough to get where you want to go. With the same logic, if it's winter and you have a low ambient RH around 35% and your sensitive ivory needs 50% relative humidity, you don't want to put in 50% gel. You'll need to pull it up with 60% or something like that. These numbers can be worked into that big equation and that's going to provide you the most helpful guide to quantities. When using a Sorvent on exhibit, the vitrine design will heavily influence the ease or difficulty in installing and maintaining the environment. The National Park Service Exhibit Conservation Guidelines CD-ROM nicely diagrams a variety of ways to incorporate a silica gel chamber into a case. Design number one requires access through the display chamber, which is the least desirable style as you'd have to deinstall the artifacts to maintain the gel. Most experienced exhibit fabricators have worked these ideas into their standard case design. Your case design also has to provide for adequate air circulation between the environmental chamber and the between where the artifacts are placed. This is often done either by having a gap around the display deck, as you see on the examples on the left, or by perforating the deck and then perhaps covering it with a textile or something else that's permeable. You want the air exchange rate between the Sorbent and the artifacts to be higher than that of the interior of the case and the exterior ambient conditions. Otherwise, you won't see much benefit. I would say to my knowledge, there isn't any specific amount of guidelines on how big that gap should be. Generally, it's considered the more the better. This is a test in a vitrine where we weren't seeing any effects from the gel in the environmental chamber at the bottom of the vitrine. Not only was the chamber small for the large size of the case, it had a narrow chimney connecting it to the display and there was clearly no circulation. Let me show you this on the next picture. This is an example of how some of those diagrams might look in an actual display case. On the left here, you're seeing doors open to the bottom of the case, the bottom of the vitrine, exposing this inner environmental chamber. This would be an example of the NPS Guidelines design number two, which has a removable and as you see sort of in that top, an inset picture, nicely gasketed access panel. But if you look at the size of that chamber in relation to the footprint of the whole deck, you'll see it sort of small. To make matters worse, sort of peeking here in the center above this lock is a chimney that connected this chamber to the deck above. This sort of had the effect of further choking off the airflow. So if we go back to this picture, what we were doing here with the test, we placed the silica gel into the vitrine rather than into the chamber below to demonstrate to the fabricators that it was the case design that was the problem, not the gel itself. And on the right, what you're seeing is the nifty little sign that the curator made up to explain what was going on during the testing. So here's another example of an installation. This vitrine was being used to display archaeological iron and copper alloy artifacts. And the lender wanted the case to maintain 20% or under for the six months of the exhibit. With limited staffing, the host institution wanted it to be as low maintenance as possible. The case had a large footprint, so we put in as much dry gel as we could fit. The chamber, as you're seeing here on the top right, was lined with marble feel and it was well gasketed, and we were able to maintain it under 20% RH for the duration of the show. Here are a couple more pictures that you can see that the artifacts were placed on slant boards over these large cutouts here on the left into the deck that allowed the air to circulate from this chamber underneath up into the bonnet. The arrow in the bottom right shows where an Arten thermo hygrometer was placed to monitor the conditions. The case maintained itself with really no trouble. And this was a relatively low tech vitrine. So here you can see an example of the dramatic effect on the environment. This is a different vitrine after the silica gel was installed. Over a couple of hours, the RH dropped from the ambient conditions of 47% to under 20%. But if you looked even over the course of this sort of less than a month, there's a steady sort of creep upwards suggesting to me that the case's leakage rate wasn't quite what we had hoped it would be. So that brings us to the question of how do you know when it's time to change out and recondition your gel? Well, there are a few types of silica gel called indicating gels that use either pH indicators, iron salts, or heavy metals to create a change in color as the gel absorbs moisture. There are a few common types these days. One is the orange to green, other is orange to light, and then there's sort of the traditional blue to pink. The blue to pink change starts to happen around 30%. We see less of the blue to pink kind these days as the cobalt dichloride used to give that color was classified as a carcinogen in the European Union. You don't need a ton of indicating gel. It's generally a bit more expensive, but you can scatter some in with large amounts of non-indicating gel as a quick visual check like you see here in this jar from Talus in the bottom right. And not a big fan of loose gel as it's a pain to work with. It can be fine though in small quantities. In storage microclimates like this one on the left, a simple humidity indicator card may be sufficient to allow somebody to occasionally check when the gel needs to be dried out. If you're using cassettes or sachets, you're better off with either a monitor that you can place in the vitrine and see like these simple thermo-hygrometers on the left, or a data logger that you don't have to physically connect to like these reasonably priced Bluetooth loggers from onset or last car. You can download the data to a phone or iPad to see what the conditions are inside the case without opening it. And the arrow there in the center is showing you one of those little thermo-hygrometers in that vitrine with metals and some unstable glass. Here you can see a graph of an environmental conditions in vitrine where we wanted to bring the RH down under 30% in a gallery with an ambient RH around 48%. There was a dramatic drop when we added the silica gel, but the differential in conditions was great enough in the case not so airtight that within a week we were back over 30% RH and we had to replace the gel. The next time we put the gel in, it was drier, but it was still only two months before the interior conditions were pulled up over 30%. Listen, how about our last poll? I'm curious about whether anyone has ever asked about airtightness of the vitrine when they're making a purchase. Well, that's not much of a surprise at the answer now. There are a number of ways to investigate the air exchange rate of a vitrine and what we call case leakage. That's sort of a whole webinar topic to itself. And for anyone who's going to be at AIC's annual meeting in the spring in Unclefell, Connecticut, there will be a paper in the Collections Care session talking about a sort of simpler, easier way to measure case leakage. So if you need to recondition your gel, there's two different things that we're talking about. The first is drying it out so it can be used again as a defecant. This is easy enough even though it's potentially time consuming. Since most of us don't have fancy drying ovens like the one on the left here, you can place your silica gel beads, cassette or sachets in a regular household oven or even a toaster for gentle heating. Most gels can be heated to about 250 degrees Fahrenheit or 120 Celsius. Indicating gels may require a slightly lower temperature, so you should check with your manufacturer or vendor. And ArcSorb in particular should not be heated above 150 degrees Fahrenheit or 65 degrees Celsius to prevent cracking of the beads. So in fact, what that means is you're going to put anything sort of on the lowest heat setting in your oven or toaster. Most manufacturers and distributors do not recommend using a microwave for drying. The amount of time the drying process will take will depend on the ambient humidity and what RH the silica has become equilibrated to. So the process can take hours or even days. And so this means to be planned into an exhibition schedule to ensure that there's enough time between venues or installations where you simply need to have enough gel on hand to flop out. Adding moisture to recondition silica gel to higher relative humidity to use as a buffer is a bit more complicated. The image on the left is a shot of the gel conditioning chamber created by Art Preservation Services. What you can see in the picture is the humidity control equipment and fans that generate the target RH condition within the chamber. This setup allows for uniform conditioning of silica gel sachets because of the large surface area of silica gel that's exposed to a precise RH condition there within the sealed chamber. A couple of companies sell their own reconditioning units that you can buy. In the middle you see the large unit sold by SmallCorp. This system, which is designed to work with their sachets, can condition up to 50 kilograms of gel at a time. This unit I believe costs somewhere around $2,700. Both Gaylord and SmallCorp sell smaller reconditioning units, these little bucket kinds of setups, that range in price from $350 to $800 depending on the vendor. And they can condition up to 3 kilograms of gel at a time. So these units may save some effort on manipulating the gel, but it's important to recognize the limitations. Uniform and precise conditioning cannot be achieved by exposing a massive silica gel to a high but uncontrolled relative humidity where the weight of added water is used to determine the RH level to which the silica gel has been equilibrated. The reason is that the moisture level is not uniform within the bulk gel, and the process is prone to error because it does not take hysteresis into account. You can mitigate this to a certain extent by then putting the gel together and sort of letting it acclimate amongst itself. But it just does mean that you may have a tougher time to recondition something yourself with sort of a jury rig setup than you would if you were buying it and you can sort of then expect from a place like Art Preservation Services that you should be getting gel that really is what it says it is on the package. Up in the top right, you're seeing, you know, a sort of mock-up of a potential setup that is a diagram in the CCI bulletin. And that's something you could also set up yourself. The demystifying silica paper by WineTribe gets some calculations for other ways to recondition to a target RH, as well as some generally useful reconditioning tips. You want to spread the gel out in a thin layer as possible because, again, it's really about surface area. You want to use a fan to circulate air around the gel. If you can, you want to periodically mix the gel layers to improve their uniformity and allow for time for moisture to equilibrate with and between the gel beads, especially if the beads of different moisture contents are mixed together. So if you're taking a batch from one between, that was at one, you know, environmental level and another from a different between, you're going to want to give some time in the sort of like equilibrate themselves. Also, you don't want to add water directly to gel as it can cause cracking of the beads. If you're reconditioning or you have gel lying around and you aren't sure what it's equilibrated to, you can easily set up a simple microclimate to check what's going on. On the left, I'm just using a simple polypropylene bin with one of those blue tooth lagers to see if I've dried out the sachets as low as I need. And on the right, I drilled a hole into this Tupperware container to fit the LSX765 meter so I could check the level of these cartridges. So here's the graph from the logger in the previous slide. Number one, that sort of blue line there shows my first check of the gel. The heating that I had done brought it down from 45% to just under 20%, but that wasn't good enough for what I wanted. Number, the area sort of around number two is showing when I took out the gel to put it back in the oven and the chamber was empty. And number three shows that after the next baking, it was under 10%, which is where I wanted it to be when I knew it was done. Once your gel is dry or conditioned to the RA-21, you can use a barrier film like Marvel Seal to create bags or pouches to maintain it until it's needed. I found these resealable bags on Amazon. And on the right, you can see the Arthura Perfets stored in a similar kind of pouch waiting for use. As we get to the end, I want to just quickly touch on some health and safety issues. I said before that silica gel is generally safe for use. As with any material, it's recommended that you request and then read the safety data sheet from the supplier. When I'm working with large amounts of silica gel, I recommend using a dust mask and gloves. And that is particularly important if you're using any of that blue cobalt impregnated gel. To sum up, it's relatively simple to use silica gel as a buffering agent without knowing too much about the particular kind of gel or even how it works. But the more you demand the gel, that is, the more you need to provide precise conditions, the more you really need to delve into that MH value and know what the gel-specific properties are. There are a number of people who I wanted to think that provided images or made sure that everything I was presenting to you is factually correct. And these are the two resources that I mentioned and that are in the downloadable handout as well as the listing of the vendors. And so now I'm happy to see if there are any questions. Okay. I'll read the questions. And let me say that I'm going to revise the handout. So you can download this handout, but there'll be a revised handout when I post it on the website. And remember that the recording, the PowerPoint slides, and the handout will all be posted within the next few days on the website. And the web address for the webinar will always be the same. And I usually will post something that says that the recording has been posted. And you can listen to that anytime on free of charge. Okay. Let me get up here to the question. And I'm also going to put the evaluation link up here because I hope we forget. The evaluations are really important to us, so please be sure to fill it in. Thanks. Kate Berluson has said, is it appropriate to use a silica gel 450-gram pack inside an arm-wired to control mold? And if I have other furniture, should I use separate smaller packs inside each drawer? Well, so that's sort of a tricky question, in part because I guess you see products like this sometimes, like if you go to the Christmas tree shop or Bed Bath & Beyond where they will be selling different kinds of sorbents with the idea that you can put them in your cupboard or closet. But if we think about a microclimate and how well it works, it really does rely on having there be a limited air exchange between the outside and the inside. So the question I guess I would have for you is, are you trying to sort of control what's going on inside that drawer? Are you trying to use it to preserve the wood of the arm-wired cabinet itself? If that's the latter, then having that inside a drawer or inside the arm-wired cabinet is not really going to help you. And even for things inside the drawer, I'd say it's a limited value just because the wood itself is buffering and it's going to have limited effect. And also the mold presents a different problem, doesn't it? Yeah, sorry, I totally forgot the whole mold issue. If you are seeing mold inside a cabinet, then you have sort of one issue. But if you're dealing with mold, then probably you do need to be dealing with your sort of larger ambient environment with something like a dehumidifier. And I would imagine that an absorbent like this isn't going to be a great solution for you. Okay. Christian, I'm just going to massacre your name, so I'm just going to say Christian. What if a geologic sample of Bentonite or Marilla Knight are objects in your museum? Are they changing based on the RH of the room? If I put on my materials hat, I would say minimally. I would say yes, but that's an interesting thing that I'd have to sort of think about how fast are they reacting. So just like with any material, the organics, the hygroscopic materials, they are going to try and reach equilibrium. So those would be probably minerals that you might want to have in some other kind of container or microclimate. Catherine Cornelis says, our cases are very old and leaky. Some are jewelry counter type cases with huge gaps sealing them in the outside of our current budget. Any tips on maintaining the environment within? I'll say before you answer that that I will see if we can do a webinar in case leakage, possibly this year, because we're still getting topics, but go ahead and see if you have any answers for that. Well, I think then, Susan, we should talk about so you can know who's presenting at our upcoming annual meeting and reach out to that presenter. So this is a tricky issue. We do see these kinds of commercial counter type cases in lots of small institutions. And even the last institution I worked at, which was abroad, there was a huge gap between these sort of sliding glass panels. And so for really sensitive things like the ivory, we actually did have a small microclimate within the case. So we basically had a microclimate within our larger microclimate because the outer container just was too leaky to be any good. And it's somewhat unsatisfying because you're sort of adding another barrier between the viewer and that piece. But if you're really worried about environmental controls, that may be the most economical option. Rebecca Shuri says, excuse me, when using art sword, how do you choose between a two set beads or sheets? So for art sword or really for any of them, the question between a cassette or a bead is really a question of convenience and sort of how is it being contained within your microclimate. Do you have a pull out tray or something like that, in which case the loose bead may be fine. If you want to make it easier to be able to manipulate it, to recondition it, the cassettes are really convenient and you pay a little bit more for that. The sheets are the bead that's used to make up those sheets is so tiny. The sheet is so reactive that really my experience with the sheet is that it's really best in very small, contained microclimates. This is something like a Passport II or a microclimate for a panel painting. Otherwise, it's so responsive that it's hard to keep it potentially within an RA range where you want it. So I'd say the sheet is really for very specific applications and the cassette or bead decision is really a question of convenience for handling and installation. Louise Coffey-Webb says, which type of silica gel container is best for textiles? I'm not sure under what application if that would be for something on display or in storage. I think without having a better sense of the context, I'd say whatever allows you to create as much surface area as possible is good. Generally, we want to hide it so whether it's going underneath a deck or behind a false back or some sort of mount or something like that, whatever allows you to contain it is probably fine. Katherine Cornelli again who's in pricey talk says, using gels to buffer in storage, but I want more information experience on raising humidity. For instance, we're in the desert. Our objects come from the surrounding desert. Is it reasonable to raise the RH levels of, say, a desiccated layer leather to meet standards for leather or smaller objects? Go ahead, Susan, because I know you've had lots of experience with this issue. I'm also in the arid west and probably it's better to keep things close to the ambient that they're used to. If you raise the relative humidity and things that are not used to that, you can cause a lot of damage. And this is partly why people like CCI have, this is partly why the environmental recommendations have been relaxed because it can be very damaging. I mostly want to keep things from spiking around. So if you need to raise the humidity slightly, that's fine, but I wouldn't work to raise it tremendously. Going back to that early slide that was in the presentation about the sort of 70-50 plus minus debate. This is really what that's aimed at. And so, again, I do agree with what Susan said. I think people have been trying very hard to create environments that are right and correct without paying attention to some issues of like what is something, what has something been acclimated to over decades or hundreds or in the case of archeological materials, thousands of years. So I was recently working in the Middle East where everything there was little on the dry side. If somebody came in and said, well, your ambient RH is low, you need to raise it up, that would have caused all sorts of problems for us with metals and soluble salts and desiccated materials. So I would suspect that a lot of your desiccated leather has sustained the damage because of that process that it's already going to house and that you would have more damage by putting it in a higher-H environment that it's not used to than keeping it sort of closer to where it's acclimated. So again, I think the CCI standards and reading their material, all of which is online, it's an amazing resource. So I think some of those will make you feel probably a little bit more comfortable about what your target environmental goal should be. And along with that, in the West, in the summer we often have monsoons. One of the best ways of dealing with that is to make sure that your stuff is boxed and that you keep things closed up during the monsoons. So that's another thing to keep in mind. Alyssa Contreras says, does anybody use cold storage environments at a set RH temperature such as in a photographic video film storage to condition silica packs? So what are the factors, time, airflow, for example? I have not heard of anyone doing that. You know, for the most part when you're trying to condition your gel, you're really focused in on your relative humidity. And you know, I can say, for instance, working with sort of what you've got, I spent a year working with Steve Weintraub or Forth Steve Weintraub and flinging some silica gel. We never tried to produce dry silica gel in the height of the summer, and similarly we never tried to create 60% relative humidity gel in the depths of the winter. You're just sort of working against what nature is doing. So I'd have to sort of even think about how you could use cold storage environments to work to your benefit. But Alyssa, if you do hear about that, I think you'd be interested to know. Victoria asked a whole series of questions, and I'm going to read them together. Where do I find the EMC versus RH curves at 25 degrees C for rapid arzorb and prosorb gels? That's the first part. And she says, so why don't you answer that one and then the next group I'll put together. Well, I'd say, and it's nice to see that Jean is here, and as he answered, his technical bulletin, the CCI technical bulletin 33, gives a lot of that EMC information in the appendices. So that would be my first stop. And then Victoria goes on to say, how do I find out if silica gel meets the Nail-D436-4E spec, which is a spec that Mark McCormick-Sudart recommends in a paper on cold storage and motion picture film, which is the method they plan to use? I have to admit that I am completely stumped by that one. I'm not familiar with this standard. I'd say that you probably have to go back and look at some of the websites like Waller's website for prosorb and things like that have a lot of technical information. And so that is one of the things that I was trying to get to that the people who really know their gels are very forthcoming with that technical information. And there can be a little bit of differentiation between the numbers that someone gets and then some of the, someone who's independently testing. That's why the graphs that I showed were from the CCI publication, because I think they are acting as honest brokers. The only thing you can do is ask Mark McCormick-Sudart directly, he has a website, and he's a pretty approachable guy. Thanks, Susan. Anne McDonald says, any resources for testing case leakage if we are unable to go to the AIC conference? And like I said before, I'll see if we can do a webinar on that. But do you have any suggestions for now? Well, I think there's a good bit of literature that's been published about case leakage. I think the challenge really has been that it's not really an easy setup or something that a small to mid-sized institution was sort of going to do for a one-off case. I know that there have been some thoughts of having kits that would allow you to do them, and there were these published procedures for it. But again, it was one of these things that institutions that had more wherewithal might have done, but not as many as I think was always hoped to make it easy to have standards that exhibit manufacturers would be able to easily sort of follow. So the short answer, Anne, is that I'd say I'm really interested to see what comes of this particular paper, and I'll see what information I can provide to Susan to see how we get a great C2C care webinar on this really important topic. We're also, there is some information for those of you who have access to that National Park Service Exhibit guideline CD-ROM that I showed some of those diagrams from. There's some, you know, information there. There's stuff out there, but I am sort of hopeful that there may be sort of a new generation of procedures come in our way that might make it a little bit more accessible. Okay. Adele Aziz says, if I use silica gel with archeological metals, is there a need to condition it? So again, I think the question is, are we talking about conditioning it to a specific RH or, you know, generally with archeological metals, there's no downside to the drier the better. So for metals, we're often talking about desiccating it to, you know, taking out as much moisture as possible. So, you know, often that's, you know, sort of somewhere under, you know, 10%. And keeping it, you know, in a microclimate, whether that's like a marble seal bag or a polypropylene or, you know, polyethylene container, you know, something that's gasketed to hold it as low for as long as possible. And so then it really depends upon how, what kind of archeological metals we're talking about. What we do know about archeological iron is that the lower the better. Really, there is a difference between holding something at under 20% and under 30% with copper alloy. There's, you know, some discrepancy, should it be under 30 and under 35, under 40. But generally, I'd say, you know, you'd want to keep your stuff dry until you start to see, you know, the RH creeping up and then take it out and heat it gently again and, you know, pop it back in there. Okay. Actually, Scheiser says, could you use the food dehumidifiers for reconditioning? I'm not sure I know what a food dehumidifier is, if that's something that. It's kind of like a cabinet that has a heater in it and a fan. I think it would take a long time. If that's, you know, as opposed to something that's like creating, like, you know, freeze drying, which wouldn't be the way to go. But if what you're describing essentially sounds like a really sort of low powered oven, which sounds about right. You know, again, the issue is, you know, keeping it at that low temperature, so you're not damaging your gel. Yeah, Yenma LaRochette said, I'm wondering if she means a food dehydrator, and that's probably right. Okay. Katherine Cornelli said, again, sorry if I missed something. How do you check what RH, your recondition gel is at? So, am I able to send us back here? So, you know, these were just, you know, two really sort of quick and dirty ways to, you know, to check. And you can see it's, you know, on the left there, I just have like a jumble of stuff as I took it out of the oven. And I didn't even sort of lay it out, you know, nicely or pay attention. It was, you know, I'm just trying to get a quick sense. So, you know, so that was the, after that, you know, was the graph showing that it did seem to be down under, you know, under 10%. On the right, I'm using a slightly better container, you know, one that has a sort of better gasketed seal. And I literally drilled into the lid there, so that this container would be sort of reusable. And you could just insert that monitor's probe. It's, you know, what you're seeing there is the probe upside down into that chamber. So that just sort of depends on, you know, how fancy you want to get. But if you have sort of like a handheld RH probe, you could do that. Or, you know, you could set up one of those little R10 thermal hygrometers if you can see, you know, through the plastic and get a sense of what's going on. You just, you know, may need to wait a little bit to let your gel sort of mix up. Okay. We have eight more minutes and I'm going to move this along here. There were several questions about reconditioning and they all sort of go back to this particular slide. So I think you've covered that and I'm going to skip them. I will just say, you know, for, you know, I can see for Valerie, like, if you're taking care of the gel and not, like, overheating it, there is no, you know, sort of shelf life to it. You can continue to use it. The issue is really is, are you conditioning it to an RH, you know, to buffer within a certain zone or are you desiccating it? But there's no sort of, it's not like a battery where, you know, you have a certain number of charges before you start to wear it out. How seal does a container need to be in order to be effective in long-term storage? Well, I guess the answer is the better the feel, the longer you will be able to, you know, maintain a differential between your ambient environment and something different within. So I would expect that you would get a longer go if you're keeping things in, let's say, a Marvel seal, a barrier film bag that has a much lower air exchange rate than if you were keeping it in a drawer or, you know, even the kind of gasketed bin that you're seeing in this picture on the right. So, you know, again, within that, it's really just a question of your seal and the difference between what you're trying to achieve in that microclimate and what's going on around it. Is there a recommended or preferred brand of food containers for microclimates? So I think, I'm not quite sure how far back I'd have to go. I think it was pretty far off, but there was one slide where we showed sort of like a small polypropylene or polyethylene sort of Tupperware style container with humidity cards. That was taken from an object specialty group postprint paper, and it's available online, and they actually sort of looked at a number of different kinds of containers for use in storage microclimates. And so that would be the article that I would recommend looking at. You know, there were certain tips about things like if you, if we even just look at what I was using here, you know, on the right here you see that there's sort of like the seal. These are the lids that like clip on. It was a much thicker kind of plastic as opposed to the one here where I was just really doing like a quick check. There's no, you know, this is not a tight lid on that box. So, you know, those kinds of things make a difference. If you have a reference to that paper, if you send it to me, I'll have it. Yeah, it's in one of the slides. So, I'm going to try and do the number before I pull that up. I'll look. Okay. Anyone know if art and sword sheets have a proper side up? One side's gold and one side's gray. I have to say, I have not used the art sword sheets myself recently. The last sheet product that I used did not have a directional use. I can't answer that definitively, but I would say that if there was, I would expect that the product literature should say it. How many times can you recondition silica gel? You know, I think we've touched on that, you know, it should be indefinite, that you're not dousing it with water, you're not, you know, heating it at too high a heat, and you're not sort of grinding it into dust. Is it possible to recondition a gel by storing it in a storage place that stays around the desired RH? That's a pretty good question. Yeah. I would say that that is, you've essentially, you know, created it. It may take a while. I don't know if you've brought that gel from, you know, somewhere else. And so some of those, you know, tips from Weintraub's article about, you know, sort of laying it out so that there's, you know, good surface area and contact and things like that. But yeah, so if you keep your gel in the desired RH for a while, then you've essentially conditioned it to that relative humidity. Rebecca Jacobs says, are there any suggestions for routine monitoring of microclimate footer in storage? I guess I would want to know a little bit more about what she specifically means in terms of, you know, in terms of frequency, you know, or equipment. You know, I think. She's writing the idea of using what she says. Okay. So let's, let's give her a second to write her reply. You know, maybe I'll just jump back to Mae's question about the Zoomador module. So, you know, the slide that I showed that that was what I understand to be one of the first in C2 tests of that. And I'm amazed if you contact me, you know, directly, I'll be happy to tell you what I know about the module. Rebecca quit typing. I'm going to remind you again to do the evaluation link. In the next few days, we will have, I'll post this stuff about the copyright webinar that's coming up. And we have two courses coming up. So please take a look at the website and see if they will be useful for you. And I keep seeing that Rebecca is typing. Rebecca, if you continue typing, we'll answer this and I will add it as a trailing question in the handout. So look for the handout, the webinar, and the recording and the PowerPoint slides in the next few days. And thank you very much. Thank you, Rachel. Thank you, Mike. And we'll see you in a month. Thank you, everyone.