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Enamelling common silver and gold alloys, Page 1 Sterling silver is an alloy of 925 parts of pure silver with 75 parts of pure copper - this relatively small (7.5%) addition of copper gives silver, which is very soft and malleable in the pure or `fine' state, a hardness and rigidity which allows it to resist wear and deformation in functional items such as hollow-ware and jewellery. ( NB: silver / copper / silicon / germanium alloys ) "Sterling is the alloy most commonly used in jewellery making and silversmithing. It was adopted as a standard alloy in England in the 12th century when King Henry II imported refiners from an area of Germany known as the Easterling. The product was made of a consistent quality and came into usage as currency by 1300 when it was known as Easterling silver." from "The Complete Metalsmith", Tim McCreight Sterling silver is an excellent casting alloy and is used here as a model. The general principles articulated in these pages apply to all of those gold and silver alloys which are capable of being vitreous enamelled with standard "jewellery enamels". The casting process isn't covered here. That information is readily available from standard reference works such as Oppi Untracht's JEWELLERY - Concepts and Technology, ISBN: 0-385-04185-3. In any case it's absolutely essential for successful enamelling of castings that they be of the highest possible quality in every respect. The casting should be performed by professionals using best-practise techniques and technology, not the bloke down the street with a manual centrifugal casting setup and an old gas torch. Unless of course you don't mind ending up with a bunch of expensive fishing sinkers for the kids! It's also assumed that the reader has a working knowledge of enamelling. Successful enamelling of sterling silver castings depends on a number of variables. Many, as responsibilities of the caster, are beyond your direct control. Important among these are porosity, crystal size and orientation, and metal purity. To minimise their effects use new, unadulterated metal (no sprues or other offcuts) smelted at the right temperature in an uncontaminated crucible. A simple process known as Depletion Enrichment is used to prepare sterling silver and similar alloy surfaces which are to directly receive enamel. Regardless of whether they have been cast, stamped, rolled or otherwise fabricated, alloys such as Sterling, unlike pure silver (and pure gold), form tenacious dark surface oxides (`firescale') during firing. The surface should be treated to remove existing firescale and reduce the effect of oxidation under the enamel. |
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