Which Metal? Part 2: Weight
When designing jewelry, the metal’s physical characteristics must be considered, one of which is weight. The pure form of each of the precious metals is an element, meaning that its molecules cannot be further broken down into separate atoms.
Each has its own symbol on the periodic table. Gold is Au (for aurum, Latin for gold); silver is Ag (the Latin for silver is argentum); and platinum is Pt. Each of these elements has a definite specific gravity, which is a measurement of density (the ratio of mass to volume), expressed in a relationship to the density of water. By definition, the specific gravity of water is 1, so each metal’s specific gravity shows how much more than water that metal would weigh, given an equal volume. For example, the specific gravity of 24-karat gold is 19.32, meaning that a piece of 24-karat gold is 19.32 times heavier, and denser, than a body of water of equal volume. The specific gravity of fine (pure) silver is 10.49, that of platinum is 21.45. Therefore, a one-square-inch sheet of 20-gauge pure gold will weigh almost twice as much as the same size sheet of fine silver, but about 10 percent less than the same size sheet of platinum. Each alloy of gold, silver, or platinum will have a different specific gravity, depending on the proportions of the metals in that alloy. That one-square-inch sheet of 10-karat gold would be only slightly heavier than the silver sheet, since the specific gravity of 10-karat yellow gold is 11.6.
The weight of metal is always a concern when designing jewelry, because it will affect the wearability of the finished piece. Large earrings in high-karat gold will be heavy and uncomfortable, and could cause damage to the earlobe. Oversize brooches may sag or even tear delicate fabric. Weight also affects cost, since it will take more mass and therefore more weight of a more expensive, higher-karat gold to cast a ring than it would of a lower karat.
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