Polishing

Preliminary Finishing

After the coin blanks or "planchets" are removed from the blanking press, they are placed in a special vibratory finishing machine, which uses thousands of tiny ball bearings, suspended in a solution of soap and warm water, to smooth out any remaining rough spots.

The planchets are then gently hand-dried in preparation for striking.

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Hot Topic: The Virtues of Good Polishing

The highly reflective and mirror finish on the field of a proof coin starts with blanks of the highest quality. Imperfections in the blank will become imperfections in the coin. This makes the blanking and polishing steps critical in the maintaining the quality of the strike. Northwest Territorial Mint maintains tight inspection and quality control of these steps to ensure the quality of the coins.

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Silver

Northwest Territorial Mint: Did You Know? Silver is a very ductile and malleable (slightly harder than gold) univalent coinage metal with a brilliant white metallic luster that can take a high degree of polish. It has the highest electrical conductivity of all metals, even higher than copper, but its greater cost and tarnishability has prevented it from being widely used in place of copper for electrical purposes, though it was used in the electromagnets used for enriching uranium during World War II (mainly because of the wartime shortage of copper).