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An Explanation of Assay Acids

When it comes to precious metal testing, the acid test is the most common method used by jewelers, refiners, and others in the field. A standard acid testing kit comes with four different bottles of acid. A common question we get is “what’s the difference between the acids?”

In truth, the bottles all contain nitric acid. The difference between them is potency. Nitric acid is powerful stuff and it will quickly dissolve other metals that are commonly alloyed with gold. Gold testing kits usually come with four different bottles of acid at different potencies – one each for testing 10k, 14k, 18k, and 22k gold.

To conduct an acid test, the piece of gold in question is scraped against a touchstone. This leaves a visible streak of gold dust on the touchstone. Next, acid is applied to the streak. If the streak dissolves from contact with 10k acid, the sample is not gold. However, if no reaction occurs, then it’s at least 10k. If you apply 14k acid to the same streak and it dissolves, then the gold in question is between 10k and 14k. If no reaction occurs, then the gold is at least 14k pure or greater. The potency of the acid is increased until the correct karat level of the gold sample can be determined. Twenty-four karat gold will be completely unaffected by nitric acid – it can only be dissolved by aqua regia (a mixture of concentrated nitric acid and hydrochloric acid).

Because there are only four levels of acid potency, the standard acid test is not ultra-accurate. However, it is a great test for small batches of scrap jewelry. If you bring gold for an acid test at our storefront in the Diamond District, we can pay you up to 98.5% of the gold’s value. Don’t hesitate to contact us or stop by the storefront if you have questions about any of our gold testing methods.

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