Assaying metal contents

ColinCMR

Hi all,

Does anyone have experience with assaying for precious metals?

How is it done? and how much sample do they usually need to take from coins, rings, antiques etc?

guitarwes

Are you talking about full blown assaying or just stratch testing to check for purity?

Weiss

Scratch tests are just that--they rub the object on a touch stone, a rough piece of rock, then put a drop of diluted acid on the rubbings on the stone. It just makes a scratch across whatever surface is being tested. That means ruining (or severely damaging) the numismatic value of a coin. But for jewelry or other similar objects it's not that big of a deal--can be done out of the way like the back of a ring or a link in a bracelet.

Lots of fake everything on the market now, so gold and silver buyers who know what they're doing will scratch D E E P, or even use a file to get way down into the metal to make sure it's not just plated.

As for assaying--lots of us have shipped scrap gold and silver to refiners. They melt what is sent down and take a testing off of the final batch, if I recall correctly.

ColinCMR

Thanks for responding, but what are the exact tests? Is it chemically done? or electronically? spectroscopic?

Weiss

Depends on who is doing the testing. Small quantities of gold or silver that are in unknown form bought by your local B&M will probably be tested with chemicals. Gold is tested with Aqua Regia, a mix of hydrochloric and nitric acid. Dilute samples are applied to the gold streak on the touchstone. The higher the gold content, the stronger the acid needed to dissolve it (I think).

I've shipped trashy scrap to Midwest Refineries, who use a similar but more intensive process.