Please Cameo Help Needed

by Thomas Leslie
(Fountain Inn, SC, USA)

A friend (he's 86) gave my wife a cameo his wife owned when she was alive. Other than the fact that he gave it to his wife about 40 or 50 years ago and it has a silver back and chain, I can't offer much more info.

If you could possibly tell me how much it's worth and possibly anything else about it, just by looking at the picture, i would greatly apreciate it.