Back in the mists of time I was Chief Electrician (in charge of lighting and sound) at the Sherman Theatre in Cardiff. One day we had loads of kids in and were giving classes as part of a Duke of Edinburgh award scheme. I'd just been demonstrating how a gobo works - thin sheets of metal placed in front of a spotlight which project designs onto a set via cutouts in the metal - when I went to change the design and unthinkingly took hold of it with my left hand.
Unsurprisingly it was excessively hot and burnt two fingers and my thumb, in fact the design - the New York skyline - got embossed onto them. I yelped and stuck my hand under the cold tap, except... just at that moment Prince Edward walked in, representing the Duke. Thankfully I could shake hands with my right hand and three minutes later plunge my left hand back in cold water again.
The embossing was still visible on two fingertips over a month later.