The prefixing of this question by the words "on silver" may have caused confusion in some quarters. Assay is by no means limited to silver; according to Wikipedia, "Services provided by [the Birmingham assay office] include nickel testing, metal analysis, plating thickness determination, bullion certification, consultancy and gem certification. Platinum was brought within the Hallmarking Act 1973."
(The last sentence is gobbledegook, but I think we know what they mean.)
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