[icydash]

Hey guys.  So let me preface this with the fact that I'm an electrical engineer, and have very little working knowledge of chemistry.

I came up with the idea for an invention, but I'm stuck on the chemistry part of it, which I was hoping you guys might be able to help me with.

Basically, I'm looking for a liquid that turns (preferably from green or clear) to red when exposed to heat above about 120 degrees F.  The transformation should be relatively quick (less than 30 seconds), and when the temperature goes back below the 120 degree range, it should go back to its original color.

Anyone have any thoughts, comments, suggestions, ideas / etc??

Thanks a lot!

[Arkcon]

The Omega corp. has sold temperature indication paints since I was a kid.  (My aunt worked for them, and used to give me catalogs.)  Since you want a reversible color changer, maybe you want a liquid crystal indicator.

http://www.omega.com/toc_asp/sectionSC.asp?book=temperature&section=f