[ThomasJperiodical]

Hello,

My name is Thomas, and am very curious about chemicals. I'm doing some at home experiments with my young children and trying to see if any non-harmful chemicals can be sprayed from a plastic dispenser (air tight) and turn a color once hitting the air (oxygen), but then turn Clear when the chemical has become dry. Does anyone have any insight on this?

My chemical knowledge is pretty minimal - but I thought I'd try reaching out to everyone on here!

Thank you,
Thomas

[jeffmoonchop]

You would probably need something that is already the colour. If the air makes it change to a colour then it will stay that way because the air will continue to react with it until it dries. Better to find something that is already a colour which reacts with the air to turn transparent and also dry it. Im guessing you want it to be an adhesive or something? Maybe think about using a coloured solvent which evaporates away as it dries. But solvents are usually not coloured and would require a pigment which would not evaporate away.

[Corribus]

Cobalt (II) chloride is blue in the anhydrous form but changes pink in the presence of water. This chemical is often used as an indicator in desiccants (e.g., silica gel). As a bonus it's pretty safe to handle and easy to find commercially. E.g., here is the hydrated form, which you should be able to dry (turn blue) by heating in an oven.

http://www.amazon.com/Cobalt-II-Chloride-Hexahydrate-grams/dp/B00IS8QDR0

Placed in a moist environment, it will change back to pink again.

It's not exactly what you are looking for but it seems from your intended use that the actual colors involved don't really matter.

I do not know of any similar compounds that change from blue to colorless in the presence of water, but that doesn't mean there aren't any. There are a lot of indicators that change colors in the presence of water and oxygen, but a lot of them require synthesis or fabrication in a lab.

NB: Copper 2 sulfate, which is experiencing a lot of interest right now by the art community (look here), will change from grayish white (anhydrous) to deep blue (hydrated), so this might be another option. You can do a lot of other neat experiments with this chemical as well.

http://www.amazon.com/Copper-Sulfate-Pentahydrarte-99-Crystals/dp/B007HU4Y5I

[billnotgatez]

https://www.yahoo.com/makers/these-magical-street-murals-appear-1292402579808310.html


Maybe the above link may be of interest

A group of designers painted giant murals in the streets of Seoul, South Korea, that appear only when it’s raining.