Thought this would be an entertaining question...
We all know the basic principles of a thermal receipt printer - it doesn't actually print anything onto the receipt paper, rather the paper is exposed to some kind of radiation (light? heat? something else? I'm not actually sure) which that causes parts of it to turn black.
These receipts fade out over time and eventually you can't read the text anymore, especially if you leave the receipt in your wallet for a long period of time.
As a result, many people, particularly small business owners, get into the habit of photocopying these receipts before filing them away for tax or expense recording purposes so that they're still legible years later.
But why, exactly, do they fade back to white? What's going on at a scientific level?
Is the plastic actually changing color back to white? Is it just rubbing off? Is it exposure to the sun that causes it to fade?
A corollary to the question would be: Would the label fade out even if you stored it safely in a cool, dark place? What can you do to preserve the label without photocopying it?
Thanks in advance for the discussions!