Karat Proportion of Alloys (other metals)*
*There are as many ‘recipes’ for gold alloys as there are manufacturers. Some White gold pieces may have Nickel, Zinc, Copper, and Manganese. Palladium is now a more popular alloy for white gold, mainly due to a high incidence of nickel allergy. (Nickel is the leading metal allergy) The Palladium alloys are not as white as the Nickel, and require more frequent Rhodium plating. Most alloys contain some Zinc for better workability. Other casting alloys may contain Silicon for a bright finish after casting. Every time these alloys are melted, some of the elements burn away, and this affects the color, workability, and ultimately the fineness of the product. This is why it is better to start with fresh metals when creating a custom piece.
The alloys are added to the gold and melted together in strictly controlled proportions. All manufacturers are required to be within very tight tolerances. Our company spot checks these tolerances periodically to assure quality. These tests are what is called a “fire assay”, in which the pieces are actually melted down & destroyed for the sole purpose of quality assurance.
While the minimum legal standard of karatage for gold is 10K in the United
States, that standard varies from country to country. Some of the commonly
encountered minimum legal standards of karatage are listed in the following
Platinum Group Metals:
The platinum-group metals (PGM) comprise six closely related metals: platinum, palladium, rhodium, ruthenium, iridium, and osmium, which commonly occur together in nature and are among the scarcest of the metallic elements. Along with gold and silver, they are known as precious or noble metals. They occur as native alloys in placer deposits or, more commonly, in lode deposits associated with nickel and copper. Nearly all of the world's supply of these metals are extracted from lode deposits in four countries--the Republic of South Africa, the U.S.S.R., Canada, and the United States. The Republic of South Africa is the only country that produces all six PGM in substantial quantities.
Platinum jewelry is usually 90 to 95% pure Platinum. The other 5 to 10% is most likely another one of the Platinum Group Metals alloyed to give strength. To be stamped simply ‘PLAT’, the fineness must be at least 95%. New markings adopted just within the last decade are ‘PT950’, and ‘PT900’. You may see older pieces that are marked ‘10% IRID PLAT’ for the 10% Iridium 90% Platinum alloy. Another popular alloy is 5% Ruthenium 95% Platinum.
Occasionally, 5% Cobalt alloy is used for castings in Platinum. This alloy is more fluid at the very high temperatures needed to melt Platinum, and works well for intricate pieces. It is also slightly magnetic! Special care must be taken by the jeweler to make sure the steel filings are cleaned away from the work before soldering.
Just like the gold alloys, it is impossible to determine by looking at a piece, just what other metals are used, unless they are specifically marked. The fineness is always strictly controlled and constant, and with Platinum, using Platinum group alloys, the metal is very pure indeed.
Rhodium has a particular affinity for dissolving in acid solutions. This makes
it ideal for electroplating, and is used on almost all white metal jewelry.