Here is a very interesting page that contains information on the content of various metals:

Metals Information -- About Metals and Platings.

It tells, for example, what alloys are used to make various types of gold, sterling silver, brass, surgical stainless steel and other metals used in jewelry-making. It addresses allergies to these metals. It tells what plating is and where lead can be found in jewelry.

It's a good basic resource for metals.

Debra :-)