The approach that the Romans used to give their base metal coins a silver appearance is highly informative.
The Roman Mints in the earlier periods of the Empire I suspect, did, in fact, use the fouree method of placing the base metal blanks in a bath of molten silver, or silver rich alloy, then stuck.
The plating on these coins looks rather thick, certainly more so than on the plated coins of the 2nd Century. I had always suspected that some lead and tin may have been included in the alloy.
Even the official Roman Mints, on occasion, for whatever reason, produced plated coins in the late Republican and early Empire. The population suspected what was going on, and to counter this, the mints produced serrated denarii occasionally.
In modern times, the .500 fine silver coins of Great Britain and her colonial possessions were subjected to an acid pickling process (blanching), before being struck. The .500 coins are made from 'Quaternary Metal', which is an alloy of 500 silver, 400 copper 50 nickel and 50 zinc parts per 1000.
The base metals of the blanks were leached out of the surface in the pickling process, leaving a spongy nearly pure sliver surface layer. The blanks were then thoroughly rinsed. The spongy surface was re compressed during the striking process, and less striking pressure was required.
The Incas also used an acid enrichment process on their gold objects. They found that gold alloy was stronger and harder. After pickling for surface enrichment of the gold, the surface was reworked with hand beating.
Posted 10/15/2011 10:12 pm
