Fire Assay | wealthymatters

Acid Test For Gold

January 22, 2011 7 Comments

All that glitters is not gold .Assaying determines just how much of that glitter is gold.

The simplest way in which jewellers roughly estimate the purity of gold is by using a touchstone.This method has been in use since ancient times.A touchstone is a small tablet of dark stone such as fieldstone, slate, or lydite which has a finely grained surface on which soft metals like gold leave a visible trace. Because different alloys of gold have different colours , depending on the different metals added to the gold and their quantities , the test sample can be compared to samples of known purity to estimate the gold content of the sample.Additionally, the fact, that the trace from the test sample will react differently to specific concentrations of nitric acid or aqua regia, can be used to estimate the quality of the gold.Unfortunately using a touchstone involves scratching the sample and each time the test is performed a tiny bit of gold is lost.And the results obtained by this method are not considered conclusive.

To avoid scratching gold,especially finished jewellery, we can use X-Ray Fluorescence Spectroscopy (XRF) which is a non-destructive technique used to identify and determine the concentrations of elements.This is the technology used in the carat meters,like the picture on the right, found in places like the Tanishq showrooms. But carat meters only assesses the metal 5 mm from the surface . So they can detect only surface adulterants.Also the machines do not identify a metal unless a sample has been fed (calibrated) into them.This is why for a long time iridium and ruthenium adulteration went undetected in India.

The only fool-proof method of determining the purity of gold is to go in for a fire assay. This is the method used in various BIS certified labs to conclusively establish the purity of gold.Unfortunately it is a destructive test. Read more of this post

Filed under Precious Metals Tagged with Acid Test, Adulteration, Aqua Regia, Assaying, Carat meter, Fire Assay, Gold, Gold Investment, Gold Purity, Investing In Gold, Iridium and Ruthenium, Touchstone, X-Ray Fluorescence Spectroscopy, XRF.RandomBlog2011

The Dirty Truth About Indian Gold

January 21, 2011 7 Comments

Here is an article that appeared in the TOI in Jan ’09.If you invest in Indian gold jewellery,this article might just persuade you to have a fire assay done on your hoard to determine its fineness.

ALL THAT GLITTERS IS NOT GOLD

Your wedding jewellery may not be as pure or as precious as you think it is. Several goldsmiths across India have taken to adulterating the precious metal with iridium and ruthenium,and are getting away with it, as until recently the metals failed to show up on all purity checks. It’s an alchemist’s dream, and the practice is becoming increasingly commonplace if you go by the stocks of the ‘duplicate’ metals at even the smallest of karigar workshops.

Both iridium and ruthenium belong to the platinum family of metals, and when mixed with gold, do not form an alloy but sit tight in the yellow metal.

What makes the adulteration even more alarming is that the metals do not replace silver and copper, which are added to the gold during the jewellery-making process to harden the soft, malleable yellow metal. As Saumen Bhaumik, general manager (Retailing) at Tanishq put it, “The two metals manage to camouflage as gold.’’

TOI tested several pieces of jewellery, and all had some amount of either iridium or ruthenium lurking inconspicuously with the gold. A 22-carat gold bangle bought in 2003 from a century-and-a-half-old jeweller—who has since then expanded from Mumbai to other parts of the country—when tested at the Indian Institute of Technology-Bombay, had 3% iridium in it.

A gold chain bought from a shop in Bangalore in 2002 when tested at another citybased centre had 2.39% ruthenium, while a pair of earrings from Kerala was found to be adulterated with 4.65% of iridium.

On an average, a piece of jewellery or a bar of gold contains nearly 5-6% of the adulterant, and manufacturers—wholesalers and retailers across India—are aware of how rampant this notorious practice is. Consumers, however, are the biggest losers as they have been kept in the dark. Read more of this post