The modern way of denoting the purity of silver, gold and platinum alloys are through a system called “millesimal fineness.” This system denotes fineness which is a measure of the weight of the relevant precious metal in its purest form per 1000 parts.

Millesimal fineness is normally expressed by making use of decimal hallmark stamps in the form of 925, 958, 999, etc.  E.g. a silver alloy that’s denoted as “925” contains 92.5% silver and one denoted as “958” contains 95.80% silver.

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