[many944s]

Check here:
http://www.ishor.com/contents.htm

They used to sell an electrolytic "pen" that had a felt tip that was impregnated with a salt solution. Off the back end of the pen was a thin wire. (they used to be sold on Ebay all the time)

To use it, you simply held the wire to the bottom of the metal you are testing, then run the pen tip over the top surface of the questionable metal. Next draw a line with the pen tip on a white piece of paper. It will leave different colored lines for different purities of various metals (Platinum, palladium, gold, etc) I think I still have one around here, I will see if I can find it and post a pic.

Hope it helps,
Nick