Fur Discoloration On Dogs My Dog's ID Tag Is Dyeing The Fur On His Chest...?

My dog's ID tag is dyeing the fur on his chest...? - fur discoloration on dogs

Our Corgi has a white fur on his chest and a plate (rabies, ID's, and license) is a slowly gray / black. Therefore, two questions:

1) What kind of metal is the source of the discoloration of the skin? If I buy a new label, I will not make the same mistake.

2) How to use your resources to ensure that the money be stopped? I have heard clearly works put nail polish, but nothing else?