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.
An example of this is the qualitative or quantitative assessment of a metal or an ore that is extracted out. An illustration of this is that gold, when extracted out, is purified to take out a normal quality, a good quality, and an excellent quality. Another example is where crude oil is taken for fractional distillation and substances like petrol, diesel, coal, normal use oil is taken out from it.
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.
The third application of this word is in medical laboratories where doctors do an immunoflorescence assay of the DNA and it is used in finding out maternal and paternal relations, finding out genetic abnormalities, cross matching procedures, determining the absence or presence of a banned substance in the bodied of sports players and in forensic criminal investigations.
When the button exhibits the weight, it still comprises of other metals that it has earlier in the ore. Therefore, to make the measurement accurate, it is important to determine the quantity of gold present in the ore. It is then stirred into the dilute nitric acid. Except for gold, all other metals would dissolve and there would be a residue left behind that would not have dissolved, and the remainder is what is called pure gold.
The leftover residue is then filtered out and is weighed again. It is weighed onto the filter paper and an extra sheet is added to determine the weight of the filter paper. The difference is the actual weight of gold in the ore.
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