The Gem and Jewelry World's foremost Resource
on The Internet. Open to the public, Free of Charge! We are here to build a strong pool of
information for the benefit of Web's jewelers and craftsmen - and those
interested in jewelry and gemstones.
Standard yellow gold alloys which are based on gold-silver copper can be used for many production processes. They could be called ‘all-purpose’ alloys. However, optimising the alloys for the particular manufacturing process to be employed is possible by use of other alloying additions which can influence relevant properties such as castability and grain size as well as the mechanical ones, for example, strength, hardness and ductility. Only a few elements (e.g. zinc, silicon, iridium, cobalt) have proved to be useful additions for modifying carat gold alloys without detrimentally changing other relevant properties.... (2002) Complete Story
The small-medium scale refiner (typically up to 3-4 kg per batch) tends to adopt the Aqua Regia process as being a relatively straightforward technique, capable of producing gold with a purity in excess of 99.9%. The essential steps in the process are to dissolve the refinable material (such as jewellery process scrap) in aqua regia, a mixture of strong nitric and hydrochloric acids, and to selectively precipitate the gold from the resulting solution.... (1999) Complete Story
A very high percentage of investment casting defects can be directly or indirectly attributed to the design of the sprue system feeding metal to the pattern. Defects such as incomplete pattern filling and shrinkage porosity are easily identified as directly related to poor sprue design. Gas porosity might be caused by a poor burnout but it could also be caused by casting at a higher than necessary temperature. And the elevated temperature could be necessary for complete pattern filling through an inadequate sprue system; this is an example of the sprue system indirectly causing a defective casting.... (2002) Complete Story
Tarnishing is superficial corrosion of the carat gold surface and is evident by a usually dark discolouration - the tarnish film. Pure gold, of course, is not susceptible to tarnishing and this property is generally not greatly reduced by alloying to carat golds as long as the gold content is high enough.... (2003) Complete Story
