Green hands and green horns

A couple of years back, one of my AP chemistry students asked me if I knew why her hand turned green when she played the French horn.

It wasn't something I was familiar with, but I had a decent guess that green on the hand was a reaction with something copper-based...and brass is certainly copper based.

With a little looking up and finding the various brass compositions used in brass instrumentation - 67-89% copper in the brass used, I feel pretty certain that it's the copper corroding and creating that green residue - on the instrument and on the hand.

My student - MK of the Eastman School nowadays - said that she tried one of the suggested solutions -  lacquer on the horn - and didn't care for how it changed the tone of the instrument. If anybody has a better suggestion, I'll pass it along to MK.