Gold purity is commonly shown as 24K, 22K, 999 or 999.9+, But these numbers cannot be confirmed by looking at the colour, shine or weight of gold. They need to be tested. This testing process is called gold assaying. The result of which helps determine its purity and supports processes such as refining and hallmarking.
Assaying, in simple terms, is the process of testing a precious metal to determine its purity. For gold, the test measures how much of a sample is pure gold. The remaining portion may contain other metals. Purity is usually expressed as karat or fineness. For example, 24K gold is a high-purity form of gold. A fineness of 999.9 means the gold is 99.99% pure. Assaying gives a measured purity result instead of relying on appearance alone.
The process depends on the type of gold and the testing method used. It usually begins with examining the gold or taking a small sample. The sample is then tested to identify its composition and measure the amount of gold present. Some methods do not damage the gold. Others require a small sample to be removed for testing. Once the test is complete, the purity is recorded as fineness or karat. Accurate results also depend on correct sampling, calibrated equipment and proper testing procedures.
There are several ways to test gold purity. Each method works differently and is used for a specific purpose.
Touchstone testing is a traditional method used to estimate gold purity. The gold is rubbed against a dark testing stone to leave a streak. The streak is then tested using reference samples and suitable solutions. This method is useful for a quick check. However, it gives an estimate rather than a precise laboratory result.
X-ray fluorescence, or XRF, uses X-rays to identify the elements present in gold. The main advantage is that it does not require cutting or melting the gold. This makes it a non-destructive testing method. XRF mainly checks the composition at or near the surface. Another method may be required when a more detailed analysis is needed.
Fire assay is an established method used to determine gold content. A small sample is heated under controlled conditions. Other materials are separated from the precious metals, allowing the gold content to be measured. BIS specifies the cupellation or fire assay method under IS 1418 for testing gold in bullion, alloys, jewellery and artefacts. Since a sample has to be removed, fire assay is a destructive test.
Laboratories may also use spectrometric analysis, ICP testing, X-ray analysis and chemical assays. The method used depends on the sample and the level of detail required.
Assaying and hallmarking are related, but they are not the same. Assaying measures the purity of gold. Hallmarking shows that an eligible gold article has been tested and marked under the applicable BIS system.
In India, BIS-recognised Assaying and Hallmarking Centres test gold jewellery and artefacts before hallmarking. Hallmarked jewellery carries the BIS mark, purity in karat and fineness, and a six-digit alphanumeric HUID.
The rules are different for bullion. Mandatory BIS hallmarking does not apply to gold coins or bars. BIS allows licensed refineries or mints to hallmark bullion and coins of 995 or 999 fineness under a voluntary scheme.
So, 24K bullion does not require mandatory BIS hallmarking. Its purity is established through assaying and refinery-level quality controls.
An assayer tests precious metals to determine their purity and composition. The work includes preparing samples, conducting XRF or fire assay tests and reviewing the results. An assayer also needs to follow set testing procedures and use calibrated equipment.
The term certified assayer should be understood carefully. What matters is the recognition, accreditation or credentials of the laboratory or testing facility. At MMTC-PAMP, the assay laboratory carries out fire, spectrometric, ICP, X-ray and chemical assays. It also supplies gold reference materials used by hallmarking centres in India for purity testing.
Gold reference materials are samples with a known and verified gold purity. Laboratories use them as a benchmark to check whether their testing methods and equipment are giving accurate results.
Gold assaying gives a clear answer to one important question: how pure is the gold?
Assaying measures the amount of gold present in a sample. This provides a reliable purity reading.
Purity and weight both affect the value of gold. Knowing the fineness helps assess the metal more accurately.
For eligible jewellery, assaying helps check whether the gold meets the required purity before hallmarking.
Refiners test incoming material to understand its composition. They also test the refined gold to confirm the final purity.
A purity mark such as 999 or 999.9 becomes more meaningful when it is backed by testing.
Knowing how gold assaying works helps explain how gold purity is measured and verified before it is stated. At MMTC-PAMP, assaying is part of the refining and quality-control process. Its facilities refine gold and silver up to 999.9+ purity, with positive weight tolerance on applicable minted products. MMTC-PAMP also offers 24K gold coins and bars for those looking to buy high-purity bullion. For those looking to sell old gold, MMTC-PAMP Purity Verification Centres help assess the purity of the gold before valuation.
Yes. XRF can test gold without cutting or melting it. Fire assay requires a small sample and is therefore destructive.
Yes. Fire assay is an established method for determining gold content.
Yes. Consumers can get gold jewellery or samples tested at BIS-recognised Assaying and Hallmarking Centres on a chargeable basis.
No. Mandatory BIS hallmarking does not apply to gold bullion or coins. BIS has a voluntary hallmarking scheme for bullion and coins of specified fineness.
It shows the amount of gold present in the tested sample, usually expressed as fineness or karat.
While jewellery and bullion such as gold coins and bars are among its most familiar forms, gold also turns up in places that have little to do with ornamentation. It helps electronic connections work, protects equipment in space and appears in everything from eyewear to dentistry.
Gold purity is commonly shown as 24K, 22K, 999 or 999.9. But these numbers cannot be confirmed by looking at the colour, shine or weight of gold. They need to be tested. This testing process is called gold assaying. The result of which helps determine its purity and supports processes such as refining and hallmarking.
Look closely at a piece of gold and you may find tiny numbers, letters or symbols stamped on it. A jewellery piece may show 22K 916 or 18K 750. A gold bar may carry 999 or 999.9. Hallmarked jewellery in India also carries a BIS mark and HUID.