Articles Required : Cobalt chloride, cobalt acetate, cobalt oxide dissolved in acetic acid with a little potassium nitrate, brush a sheet of paper.
You must've heard of special inks which, when used on the paper, remain invisible, and can be seen only through some special method. But, here instead of inks we are going to talk about colours that have almost similar properties. In beginning the picture made with these colours will remain invisible but on heating a little it will come to life with cheerful pink, blue and green colours.
To make such colourful pictures, prepare three solutions in separate glasses. Be careful to keep them separate even when you are using them on paper.
Your three solutions are colourless, so when you make a painting with these on the paper it would appear invisible. However, while applying the solutions you've to keep one solution from touching the other. Of course this is a difficult task, but with a little care you can do it. When you've finished with one 'colour' you'll have to wash the brush properly. When your picture is dry and you show this blank paper to somebody, he wouldn't be able to even imagine that a colourful picture is hidden therein.
Well, your main task is over and now you just have to raise the .curtain of suspense. As you bring the sheet near the fire, colourful attractive picture would emerge on your blank paper. Do you know how? Simple! Due to the effect of heat cobalt chloride will turn into green colour, cobalt acetate into the blue and cobalt oxide into pink!