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<p>[QUOTE=&quot;maridvnvm, post: 18684465, member: 31620&quot;]That Tetradrachm isn&#039;t plated or silvered it is Billon. Billon is an alloy of a precious metal, in this case silver with base metals such as copper. By the time this coin was made the silver content had dropped below 50% and could well be as low as about 30%. That doesn&#039;t mean it is plated.</p><p><br /></p><p>These billon coins underwent a surface enrichment technique to make the surface of the coin appear more like a pure silver coin. We do not know the exact method used but there are many hypotheses out there. Techniques that are proposed include segregation during casting or annealing, deliberate thermal and/or chemical post-treatment such as pickling in acids or blanching.</p><p><br /></p><p>These techniques could also be used on much lower alloys such as that used in the much later &quot;silvered&quot; coins where the silver content was as low as about 5%.[/QUOTE]</p><p><br /></p>

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