 Right. You're due to teach a lesson on acid-base indicators and you haven't got any blue litmus paper, red litmus paper, or the normal indicator solutions that we use. You're stuck. So what do you do? Are there any other ways in which you can do it? Well, litmus is nothing more than an extract from lichen that grows on rocks and that's a natural pigment. And there are plenty of other pigments in nature that we can use. Let me show you some of them and some ideas that you might want to go into. The one that most people know about is tea. It's got a natural brown color and if I just take some citric acid from a lemon and we squeeze it into the first and then some bicarbonate of soda, I put it into a solution here and we'll put it into this one. Give them a stir and clearly a very different color. Well, tea works alright but in fact we've got ones that are much better than that and flowers are one such one and this is one that I use quite often. I've got petunias in this case, lovely purple ones and all you do is you take some of those flowers, put them into a plastic bag, a little bit of solvent to dissolve that pigment. Not too much, just put a small amount in because ultimately we want to get a nice concentrated solution of the pigment and then once it's in there crush the petals up so that the solvent can be in contact with the pigment break the cells. Right, having done that we've now got a lovely pigment solution in our plastic bag. To filter it all we do is nip the corner off the plastic bag and pour it into a test tube. Here's our solution. Good, let's take a little bit of that solution into two test tubes and let's put some vinegar, citric acid into the one. Oh, isn't that cool? And let's put some handy-andy a base into the other. Maybe we need a little bit of water just to take it into solution. Isn't that beautiful? Clearly a different color in an acid and in a base that makes a very good acid base indicator. Right, so you've got your indicator solution. What about indicator paper? Well, there's a nice easy way of making that out of that. Just take a piece of filter paper or you can take tissue paper if you don't have filter paper, any absorbent paper and just pour your indicator solution onto it. Try and get this as concentrated as possible. Once that's thoroughly wet you then put that into the sun to dry and that's what I've already done and there we have it. We've now got indicator paper. Of course we can cut it up into strips just like litmus paper and use it as a test strip to test whether something is an acid or a base. So if I put a little bit of acid on it, what happens? And if I put a little bit of base on it, dry the handy-andy again, voila, we've now got indicator paper. And of course this is easy for children to make at home if they've got methylated spirits, if they got flowers. And there's a lot of lovely investigations that you can get kids excited about primary school level, even high school level. For example, around the home there's a lot of chemicals in the kitchen. You've got bicarbonated soda, cream of tartar, some vitamin C, epsom salts, table salt, handy-andy, vinegar, etc. There's a lot of chemicals at home. A lot of them are neutral, some of them are basic, some of them are acidic. Get children to go and identify. And then with respect to indicators, are all flowers indicators or just that petunia? I've got a red petunia, is it the same color change as blue? What about white petunias? Has white got color? Orange, red, blue? Do they all have indicator properties? Do the colors always change the same? Are they different? Hibiscus? I find they work very well. The red ones. I've not tried the white. Maybe you can try that. Right, I've shared with you some ideas today on the acid-base indicator properties. But there are many ideas out there that people have got and I invite you to send those ideas into me so that I can share them. I'll find ways of doing that and I will give you proper acknowledgement. And just send me the idea on this email address.