[velocity101]

Hello all!  I'm trying to help my nephew with a science experiment. The project involves creating a paper coated with a dried chemical which changes color temporarily when excited or struck. I haven't played with chemistry for a while. Is there anyone that knows how to do this with non-toxic commonly available chemicals?  Thank you so much in advance!

[billnotgatez]

Can we assume you are excluding the invisable ink and/or ultraviolet light stuff.

[Arkcon]

Sorry.  But the whole project doesn't seem plausible from an advanced chemistry point of view, and certainly not from an amateur chemistry point of view.

The project involves creating a paper coated with a dried chemical

Now paper coatings are not trivial science, and dry paper coatings, now that is hard work.  Maybe you mean something wet, that dries ...

which changes color temporarily

Reversible color-changing dyes are likewise not trivial.

when excited or struck.

You'll have to describe better what you mean by "excited."  That's just not a real chemical term.  Unfortunately, "struck" is also problematic -- a significant chemical change on a massive crystal might be possible, but you said you've coated it, on paper -- try to think critically ... how much force is the paper going to bounce back when struck to the coating?  Won't it just rip?

Maybe you should start with something more simple like billnotgatez: suggested.

[aliphatic]

Is heat sensitive ink what you are looking for? Are you trying to permiate / coat some paper, or looking for a ready made product?
http://www.ctiinks.com/product.php?proid=40&sub_catid=&page=Thermochromic-Offset

[velocity101]

Can we assume you are excluding the invisable ink and/or ultraviolet light stuff.

Correct. I want something that can be seen in normal lighting conditions.

Now paper coatings are not trivial science, and dry paper coatings, now that is hard work.  Maybe you mean something wet, that dries ...

It can be applied wet (like paint) but the end result needs to not drip off the paper. Sorry, my description wasn't originally clear on that.

You'll have to describe better what you mean by "excited."  That's just not a real chemical term.  Unfortunately, "struck" is also problematic -- a significant chemical change on a massive crystal might be possible, but you said you've coated it, on paper -- try to think critically ... how much force is the paper going to bounce back when struck to the coating?  Won't it just rip?

What I mean is that if you place the paper on the floor and hit it with a hammer; that sudden impact makes it temporarily change color.

Is heat sensitive ink what you are looking for? Are you trying to permiate / coat some paper, or looking for a ready made product

I've looked into color-changing paints, but do you all feel that something like hitting a paper coated with this stuff would generate enough heat to initiate the color change?

Thanks again for all of your replies.

[vmelkon]

IIRC, you can use lemon juice to write on paper. Once it is dry, it look invisible. When you heat it, the organic molecules from the lemon juice tend to decompose. http://chemistry.about.com/cs/howtos/ht/invisibleink3.htm

I think that CoCl2 can be used as well. While it is hydrated, it has a light pink color. When you heat it, it loses its water of hydration, it turns into a dark blue color which is easy to see.

[aliphatic]

Here's what you're looking for:
Piezochromism

Unfortunately, it looks like your project may not be possible as a one step process with current materials science. Can you adapt the project to multi layered approach? Two charged conductive layers of transparent or translucent material seperated by a thin nonconductive layer and some voltage or heat sensitive ink should work. Strike the material, complete the circuit, and Bob's your uncle - heat and color change. Those battery charge test strips that are applied to the sides of batteries are a simplified version of what you want.

Have some reasearch articles to bang your head against!
http://pubs.rsc.org/en/Content/ArticleLanding/2011/JM/C0JM03950K#!divRelatedContent

Good luck!