PRECIOUS METALS

(GOLD, SILVER, PLATINUM GROUP)
All precious metal weights are given in troy ounce (oz t); there are 12 troy ounces per pound (lb. t) in contrast to 16 "regular" (avoirdupois) ounces (oz) per pound (lb.).
Gold (Au)
Purity or "fineness" denoted by karatage (K); 24 karat gold is pure gold.
12 karat gold is 50% gold and 50% alloyed metal.
Gold will alloy with nearly all base metals (Cu, Pb, Ni, etc.); different colors of gold are produced by alloying with different base metals. Common alloys are Ni and Cu.Gold purity can be tested with inexpensive devices that measure electrical conduction, or by the older method of gauging the extent of reaction with dilute acids. Pure gold is inert with respect to dilute HCl and HNO3; most alloys will react slowly in these acids. Gold plating or filled can be detected by testing a scratch in the item.
F.T.C. Guidelines governing sales of gold and gold jewelry in this country state the following:
1) If Karatage is to be stamped on, it must be at least equal to that designated or higher, and also must be accompanied by a trademark.
2) Terms "pure gold" and "solid gold" can only be used for 24 karat gold.
3) Term "gold" can only be used if gold content is 10 K or better.
4) Term "gold filled" applies only to items composed of a layer of gold pressed (not alloyed) onto a base metal where the weight of the gold comprises at least 1/20th of the total weight of the item. Fineness must be shown by stamp, e.g. "1/20 12k G.F." means the gold layer is 12 karat gold and comprises 1/20th of the total weight of the item.
5) Term "rolled gold plate" is the same, but gold comprises less than 1/20 of total weight; e.g. stamped "1/30 12 k G.P." means 1/30 of the metal weight is from 12 karat gold plate.
6) "Gold electroplate" or "gold flash" or "gold washed" mean a gold coating that is 10 k or better gold at least 0.000007 inches thick. A variant, "heavy gold electroplate" (H.G.E.P.) is at least 0.0001 inches thick.