How to Check Gold Purity: Reliable Methods and Myths

Everyone has a story about testing gold: bite it, hold a magnet to it, rub it on a stone. Some of these tricks tell you a little. None of them tell you the purity of a piece. Here is what actually works, and what does not.

Myths that do not work

• The magnet test: gold is not magnetic, but neither are many other metals, and some fake pieces are made with non-magnetic alloys. A magnet can rule out iron or steel, and that is all.
• Biting the piece: soft metals show marks, but plenty of metals are soft. It also risks your teeth.
• The skin or colour test: colour depends on alloy, not just purity. A good imitation can look right for years.
• The float or sink test: density tests need a controlled setup to mean anything, and a plated piece can be dense enough to fool a casual check.
• Judging by weight alone: heavier does not mean purer.

None of these should be relied on for a purchase decision.

What reliably tells you purity

1. The BIS hallmark and HUID

The strongest everyday check is the BIS hallmark. It confirms that a recognised centre tested the piece. See BIS hallmark marks explained for what to look for, and how to verify a HUID to confirm the record.

2. Assaying at a recognised centre

If your piece has no hallmark, for example old family jewellery, you can have it tested at a BIS-recognised assaying and hallmarking centre. Testing methods used by centres include fire assay, the reference method for gold purity, and XRF analysis, which reads the surface composition without damaging the piece. Fire assay needs a small sample and is used where an exact figure is required.

3. Touchstone and acid tests by a trained person

Jewellers have long used a touchstone and test acids to estimate purity. In trained hands this gives a quick idea, but it is an estimate and tests only the surface. It is useful as a first check, not as a certificate.

4. Electronic testers and XRF machines at a jeweller's

Many jewellers use XRF machines to read the composition of gold. If you are exchanging old gold, ask to see the reading and ask how the figure is used in the calculation. Our article on how old gold exchange works lists good questions to ask.

Why plating matters

A thin layer of gold over another metal can pass a quick scratch test and look right. Tests that read below the surface, or a hallmark applied after assay, solve this. If a piece is cheap for its weight, plating or lower purity is worth considering.

What to do when you are not sure

1. Ask for the hallmark and HUID, and check them.
2. Ask the jeweller to explain how purity was tested.
3. For old pieces, get an assay from a recognised centre before you sell or exchange.
4. Keep the invoice, which records what you were told at the time.

Buying with fewer doubts

Our product pages list each piece's purity, so you can read it before you visit. If you would like to see a hallmark checked in front of you, book a visit to our Patna showroom. You can also explore gold bangles and bracelets and read the purity on each product page.