black receipt

     Today some section of a receipt turned black!  It had been lying under a warm tray from the oven so I figured the blackening had something to do with heat.  So I did a little research...

Blackened Receipt

    I was right! Receipt paper is made out of thermal paper which paper that reacts to heat. When you also briskly swipe a nail over thermal paper, it may may a black, blue, or red mark!