If there are no stamps, or the piece is over 18 karats, or the buyer wants to validate the stamp value of any items, we test each item in one of two ways. Coins or bars of trusted karat and weight will skip any validation at the discretion of the gold buyer.
Acid Scratch Test
The acid scratch test is where we scratch an item on a smooth touch stone (similar to slate). This makes a fine mark on the stone and does not damage the piece in any way. If this test goes well, it may be the only one needed.
If the item is unstamped, we begin with 10kt acid and compare the ‘unknown’ item to a test key (a sample of gold with a known purity). The unknown scratch should stay very bright and solid. If the scratch fades, we return the item to the client since we cannot purchase unmarked pieces that do not meet the 10kt acid test. If the scratch stays vibrant, we replicate the test with a 14kt acid. If it passed at the 10kt level but failed at the 14kt, then we know the item is 10kt. If the item passed at 14kt we continue testing with increasingly stronger acids.
If the item is stamped we compare the item to a test key at the specific karat rather than working our way up from 10kt acid. If we find that the item performs as well as the test key, we will purchase the item at the stamped karat. If the test is close, we will give the item the benefit of the doubt. If the item clearly doesn’t test well at the stamped karat, we will work to evaluate the true karat of the item.
X-Ray Fluorescence Testing
If visual and scratch testing methods do not confirm clear results, items can be tested by an X-ray fluorescence scan. The machine used for this test is an incredibly powerful state-of-the-art device capable of providing detailed analysis by measuring the intensity of the generated gold X-rays by wavelength dispersion analysis. When testing is complete, a full report indicates the percentages of gold content as well as other alloying metals such as copper, silver, zinc, etc. This method is remarkably accurate.
Specific Gravity Machine
The Specific Gravity Machine determines the purity of gold by measuring its density underwater. We weigh the item once on a normal scale and once under water. The difference in the weights determines the density of the item. Since gold is one of the densest elements, we can identify items that are gold plated and identify the purity (karat) of gold based on the density.