This is slightly embarrasing, but here we go.....I just looked
up the conversion between ounces and grams in McCreight's "Complete
Metalsmith" and found that I didn't know whether I was interested
in ounces troy or avoirdupois.
Can someone tell me the difference, and which would be the one I use
in the US for measuring precious metal?
The troy unit of measure is used to weigh precious metals. As
Americans, we tend to use avoirdupois method of weight, with 16 oz. to
a pound, however we still use troy weight for precious metals. These
two systems are antiquated, having come from methods which were used
in ancient days, which used either parts of the bodies to measure
distance (a rod was the length of a man’s fingertip to his nose), and
grains or bushels of wheat to measure weight, as these things were
commonly available to most people.
In the troy system, one grain equaled one grain of wheat. Twenty-four
grains of wheat equaled one pennyweight (the weight of a penny), 20
pennyweights equaled one troy ounce, 12 troy ounces equaled one troy
pound. One ounce avoirdupois equals .91146 ounce troy. I don’t know
what the avoirdupois method used as a measure, as the history teacher
never got around to that one. Maybe someone else out there has that
bit of trivia.
Just remember that when you’re ordering precious metals, it’s always
measured by troy ounces in the U.S. Base metals are usually ordered
by avoirdupois ounces, which is why an ounce of copper will weigh
(about 46%) more than an ounce of silver on a balance scale. However,
if you’re alloying your own metals, it’s more accurate to use the
European standards of weight in milligrams, grams, etc.