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Can an explanation please be given for calculating the purity of Early American silver using the assay marks? For example 10-15. Thank you.
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According to the Rainwater book, the Baltimore Assay office marks for 1815-1830 were 11/12 or 10.15
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There's also just a bit more info in this post ->

http://www.925-1000.com/forum/viewtopic.php?t=3161" onclick="window.open(this.href);return false;
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