The subject of testing gold for karat and genuineness has come up in a few recent blogs, and I keep mentioning the “acid-scratch” test as being one of the most reliable (of course, any test is only as reliable as the skills of the person performing it). It occurs to me that not everyone will know what the test involves, and that because of the name there might be concern about what the test does to old gold jewellery.

Often, the stamp in a piece of jewellery indicating the karat or fineness of the gold is sufficient and can be trusted. However, in cases where the stamp is missing or unreadable, or where the jeweller’s trained and experienced eye doubts the stamp’s reliability, a further test is performed on the gold material. In many cases, the acid-scratch test is used.

First, the piece of gold jewelry is rubbed on a test stone to produce a thin “smear” of gold. This procedure does not result in any visible damage to the gold item.

gold jewelry acid scrape test

Karat acids and testing stone (showing gold "smear")

After the smear is produced, acid is applied to it in decreasing concentrations to determine the karatage. If 22K acid makes the material disappear, then the gold is less than 22K. If 18K acid makes the material disappear, then the gold is less than 18K. If 14K acid makes it disappear, then it is less than 14K. If 1oK acid makes it disappear, then it is not even 10K, and likely not gold.

At Gold Guys, once we’ve have verified the Karat of a gold jewelry piece, we then weigh it (in grams) and mare an appropriate purchase offer.

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