Liquid crystal sheet
If you are looking on the internet for a sheet of plastic that changes colors 
when warmed up, you might use a search term like "thermochromic sheet", but will not find any results.
As always, even though I was sure it would be called a thermochromic sheet, you will actually zero usable results by using this term. The only results you will get is when you will realize that the "correct" internet search term for this product is "liquid crystal sheet".
Possible search terms that will not give you what you are looking for: Thermochromic, Thermochromic film, Thermochromic sheet, color change sheet
"Correct" search terms (figured after 2 hours of internet searching, which I hope you will not have to do): liquid crystal film, liquid crystal sheet. Wikipedia article
Available retailers (low quantity, high price):
Edmund Scientific
Educational Innovations (note: these come with adhesive backing to a sheet of paper. Read below how to remove the adhesive)
Omega
Anchor Optics
Edmund Optics
ThermometerSite.com
If you do buy from Educational innovations and need to take the adhesive off, spray it with Goof Off outside, and use gloves and paper towels to rub the adhesive off (rubbing off after Goof Off is simple, just keep it off your clothes and skin). A can of Goof Off is actually a must-have in the household because it can do much more, like take all of those pesky sticky labels, or even to take permanent marker off.
˅˅˅ Additional valuable information is available at one of the links below: ˅˅˅
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Page last modified 28-Jun-09 16:26:05 EDT
Comments on this page:
Author Name: MKRD.info Date posted: Nov 10, 2011
Comment: Hello Larry,
You are welcome.
Actually, that's exactly what I bought those film sheets for -- finding shorts in PCBs. I actually had to get the paper backing and adhesive off the sheets -- used Goof Off! Do it outside!
For finding shorts, you need 20-25, and 25-30 deg C sheets. 4x6" or 4x4" are preferable over larger sheets.
To not have your fingers heat up the sheets, use gloves or a piece of a plastic to press the sheet over the board, and apply a little pressure while rubbing.
You will need 5-10A power supply. Start very slowly. Reach 0.5A slowly, while making sure to inspect whole board before each current increase. Then go up if short does not appear.
Author Name: Larry Date posted: Nov 10, 2011
Comment: Michael, thanks so much for the links.
Previously to seeing this, I had only located the Omega site selling the adhesive-coated sheets.
Now I have a few companies to choose from.
I need to buy some sheets of liquid crystal film, for diagnostic purposes.
Actually I want to use it in assistance of locating shorts on a circuit board.
Which is so much cheaper than buying a good IR camera for 3k or 4k USD.
Thanks again; Larry C
. 