Tuesday 10 June 2008 — This is 15 years old. Be careful.
The weather so far this week in Boston has been extraordinarily hot: 95 degrees or so for the last three days. As graphic evidence, here is a CVS receipt I had left in a bag in my car yesterday:
This receipt is printed thermally: the paper is impregnated with a dye which turns dark with sufficient heat, and the print head in the cash register uses a tiny heating element to darken individual pixels to produce the image.
As you can see, the paper got hot enough simply from being in the car to darken substantially! I haven’t found a reference for the temperature at which thermal paper darkens, but I’m guessing it wasn’t very comfortable in there...
Come to Perth, park a car in the sun for a few hours in summer and that thing will be black. We get something like 20 days above 35(c) and 46 is the hottest we have had ;-) Those little bits of paper really suffer then ;-)
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