Silver quarter poison detector: Myth?

Factual Questions
1

I just read in a magazine about a family that fried wild mushrooms during the 1930’s. To find out if they were safe to eat, they’d put a silver quarter in the pan. If the quarter turned black, the mushrooms were considered poisonous. According to this article, no one in this family ever got sick from mushrooms. The author wanted to know if anyone else used this trick.

While I’d never do this myself, I’m curious to know if there could be any scientific basis to this idea, or if the family was just lucky. I do know that silver was considered “magic” by many people.

Also, what in the mushrooms could turn it black, if not poison?

2

Any sulfur compound.

3

this. the black tarnish that forms on silver is silver sulfide, not an oxide.

4

The poisonous compounds found in different mushrooms are very different chemically, so it is hard to believe that any test like this is a universal poison detector.