How hot was it?

Tuesday 10 June 2008 — This is more than 16 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:

A receipt printed on thermal paper

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...

Comments

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Tony Meyer 7:21 PM on 10 Jun 2008
I don't know for sure it's the exactly same printing process, but here in NZ these thermally printed receipts darken when left in the car even when the temperature is in the mid 20's (C). It surprises me a little that there isn't a little notice on the back of the paper explaining this - it really looks like the paper was just short of catching fire. Although that's not really a risk at all, it seems like people could easily suspect that.
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tim 7:33 PM on 10 Jun 2008
Hi Ned

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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johnmc 7:41 PM on 10 Jun 2008
Ned, got another observation for you. That very same receipt will fade to white in the presence of light after about 2 months. I think that is by design. Hard to return something when the receipt is blank!!
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Jay raves 7:56 PM on 10 Jun 2008
It's happened to me several times but I live in Austin TX and it can get pretty hot here.
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Grumpy Old Man 9:39 PM on 10 Jun 2008
Huh, you still shop at CVS, no wander it fades. You should probably shop at GIT or one of the newer pharmacies these days, so much better.
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infidel 3:16 PM on 11 Jun 2008
Feh, in Phoenix we've had overnight lows that were hotter than that :-P
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peter 7:08 AM on 12 Jun 2008
Interesting which parts darkened. How was the receipt positioned in the bag? Exposed, completely covered, or near something else that heated up?

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