How to check gold purity — XRF, hallmarks and home tests
If you are about to sell gold, purity is the single number that decides your payout. A 5% error on 50 grams is roughly ₹39,000. Here is how purity is actually measured, ranked from most to least reliable.
1. XRF assay — the standard
X-ray fluorescence bombards the metal with low-energy X-rays and reads the fluorescence each element emits back. Because every element has a unique signature, the machine reports exact composition — gold, silver, copper, zinc — in seconds.
- Non-destructive — no scratching, no acid, no melting.
- Accurate to roughly ±0.1% on karat gold.
- Visible — a good jeweller shows you the screen.
2. BIS hallmark — what it does and does not prove
A BIS hallmark with a six-digit HUID certifies the piece was assayed at a licensed centre. Look for the BIS logo, the purity mark (916, 750, 999) and the HUID. You can verify a HUID in the BIS Care app. It is strong evidence of purity at the time of hallmarking — but it says nothing about repairs or solder added later.
3. Acid / touchstone test — outdated
Rubbing the piece on a stone and applying acid gives a rough band, not a number, and it removes a small amount of metal. If someone offers only this before quoting, treat the quote as an estimate.
4. Home checks — useful screening, not proof
- Magnet: gold is not magnetic. Attraction means significant base metal — but a non-magnetic fake is easy to make.
- Density: pure gold is 19.3 g/cm³. Weigh, then measure water displacement. Tungsten fakes defeat this.
- Discolouration at clasps and edges suggests plating.
Before you sell — a short checklist
- Weigh your gold at home so you know the number.
- Insist on XRF in front of you, not in a back room.
- Ask for the purity in writing before any price is discussed.
- Ask exactly what deductions apply and why.
ABRAF assays free, on screen, with no obligation to sell.