The specific gravity test for silver.

How to do it

1. Weigh the piece dry, in grams. Call it A.
2. Hang it by a thin thread in a cup of water on the scale, so it's fully under water without touching the sides or bottom, and read the weight. Call it B. (On a scale with the cup sitting on it, tare the cup first, then the reading with the piece hanging in it is the weight of water displaced, A − B.)
3. Specific gravity = A ÷ (A − B).

Example: a piece weighing 31.10 grams that displaces 2.97 grams of water has a specific gravity of 10.47, right for fine silver.

What the numbers mean

Getting it right

• Scale resolution: a 1 ozt piece displaces only about 3 grams of water, so a scale that reads to 0.01 gram gives an answer within about 0.3%. A small piece needs a more precise scale.
• Air bubbles: a bubble clinging to the piece makes it read light. A drop of dish soap in the water helps.
• Water temperature: water's density changes slightly with temperature; at room temperature the effect is small.
• Hollow or weighted pieces: filled handles, candlesticks, and stones throw the number off completely.

What it can't tell you

Specific gravity is the average density of the whole piece. Molybdenum is within about 2% of silver, and a counterfeiter can combine a heavy metal like tungsten with a lighter one to hit silver's number. A piece that passes is consistent with silver; it isn't proof.

Sources

• Densities from the CRC Handbook of Chemistry and Physics via the University of Waterloo, and alloy densities from Stuller.
• A&D Company, AD-1653 density determination kit manual (method and error sources).

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