Assay means the analysis of precious metal component in an alloy, a piece of art or jewellery. This is a very technical job, and it is carried out only by authorized institutions that have the right and relevant equipment to test the precious metal content. Such institutions are called Assay Offices. After performing the necessary procedure of assaying bullion, they certify the claim of the maker about its quality/purity by stamping a Hallmark on it.
Hallmarks are special symbols that stand for some specific thing. For example, a 750 stamp means 18k gold; and 999 means 24k gold. There are a lot of methods for assaying gold or bullion: the touchstone method, X-Ray florescence and Cupellation. Each of these methods determines the fineness of the gold product, as claimed by the manufacturer.
The Touchstone method is employed in cases where the product under analysis is extremely rare or precious. Touchstone is a special assaying tool which determines the fineness of the product up to 10 to 20 parts per thousand, precisely. The product under question is rubbed with the touchstone and then removed. The touchstone is then treated with acids or chemicals and the colour difference is studied with the help of references.
This process, however, is not recommended for white gold analysis because the colour variation among the white gold alloys cannot be differentiated that easily. This is one of the oldest methods of assaying gold and bullion.
X-Ray florescence method is a latest and very quick method of assaying gold products. It is also used mostly on precious gold pieces which cannot be destroyed by other methods of assaying. This method is ideal for flat and large surfaced products. It doesn’t take more than 3 minutes to test the metal and it generates a computer print of the test result.
Another advantage of this method is that it tests the composition of the other components present in the alloy. There are some contraindications for this method as well. Those gold products that are treated with chemicals or have gone through electroplating should not be assayed with this method.
The most accurate method of assaying gold is Fire Assaying or Cupellation. This is also a completely destructive method of assaying. It gives the fineness of 1 part of gold per thousand accurately. This is an internationally recognized method of assaying and is used commercially for assessing the quality of gold ores. Major refineries and gold mining companies use this method for analyzing the purity, fineness and quality of gold ores.
Gold and silver coins are also assayed by the appointed assay offices. This was important at a time when gold and silver coins were uses in daily commerce; nowadays, the use of gold and silver coins as currency is suspended in many countries of the world. But gold coins are still available for small scale investment purpose or as a means of exchange of gifts on special occasions. There are local gold assay offices everywhere in the world that can find out the purity of the gold products which you wish to get assessed.
Source by Jack Wogan
What Does Assay Mean?
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