the (un)real thoughts of realbt

I have a thermal printer sitting atop my desk at work. Actually, it’s sitting atop my tower that is lying on it’s side (but that’s another story). I have an Epson thermal partial-cut receipt printer. It’s pretty cool, this little thing. But what I really want to know is: how the hell do thermal printers work, and why is it that after a while, the thermal print on the (thermal) paper fades away? I used to have a thermal fax machine, and the print would just sort of randomly fade away if left long enough. It’s odd.