2-13. FINENESS, CARAT, AND WEIGHING
The amount of gold in a gold alloy may be rated in terms of fineness or carat.
Fineness is determined by the parts per thousand of pure gold contained in the alloy. In
terms of fineness, pure gold is 1,000 fine and an alloy with three-fourths pure gold is
750 fine. In the carat system of rating, the carat refers to the parts of gold determined
by dividing the substance into 24 units and then counting the number of units of gold.
Thus, a 24-carat substance would be pure gold and a 12-carat alloy would be one-half
gold. In weighing precious metals like gold and platinum, the troy system of weight is
used. In this system, the basic units of measurement of alloy quantity are grains,
pennyweights, and ounces. Gold alloys are recorded and issued by the troy system as
indicated in Table 2-1.
24 grains (gr)
1 pennyweight (dwt)
20 pennyweight (dwt) =
1 ounce (oz)
12 ounces (oz)
1 pound (lb)
The conversion formula for carat to fineness is:
Table 2-1. Troy system of weight.
Through the use of controlled heat and rate of cooling, gold alloys can be
annealed (softened) or tempered (hardened). Gold alloys are hardened by slow
cooling. Rapid cooling from a high temperature will soften a gold alloy. Rapid cooling is
done by quenching the heated gold alloy in tap water.
2-15. GOLD FOIL
Gold foil is a restorative material used in the pure state. It is used most often on
facial surfaces, proximal surfaces of anterior teeth, and occlusal surfaces of posterior
teeth. Its chief disadvantages are color, high thermal conductivity, and difficulty in
manipulation. Gold foil is available in either adhesive or nonadhesive form. To prevent
pellets of adhesive foil from sticking together before use, their surfaces are treated with
moisture or gas residues. When ready for use, the moisture and gas residues are