Buying guide
How to check gold purity in India: hallmark, HUID, karat meters and XRF testing
Start with the hallmark: the BIS mark, a grade such as 22K916 and a six-character HUID that you can verify in the BIS CARE app. For a piece without a hallmark, or old gold you are buying, a non-destructive XRF test, often called a karat meter, reads the purity in under a minute. Fire assay at a hallmarking centre is the reference method. Home tests with a magnet, water or vinegar cannot tell 18K from 22K.
· 7 min read · By Dhyey Mehta
There are two ways to know how pure a piece of gold is: read what has already been tested and marked on it, or test it yourself. For most jewellery sold in India the first is enough, because the BIS hallmark already records the result of a laboratory test. The second matters when a piece has no hallmark, when you are buying old gold, or when you run a counter, a workshop or a gold loan desk.
This guide covers both, in the order a careful buyer or jeweller would use them. The hallmark details follow BIS sources; for the full rules, see our guide to HUID hallmarking.
Step 1: read the hallmark
A gold hallmark in India has three parts:
- The BIS standard mark, the triangle logo.
- The purity grade and fineness, for example 22K916.
- A six-character HUID, the code that identifies that one piece.
The number after the K is the fineness: the minimum parts of pure gold in every thousand parts of metal. BIS lists seven gold grades:
| Grade | 9K | 14K | 18K | 20K | 22K | 23K | 24K |
|---|---|---|---|---|---|---|---|
| Minimum fineness (ppt) | 375 | 585 | 750 | 833 | 916 | 958 | 995 |
So 22K916 means at least 91.6% gold, and 18K750 means at least 75%. If the grade on the bill does not match the grade on the piece, ask why before you pay.
Step 2: verify the HUID in the BIS CARE app
A hallmark can be copied; a HUID can be checked. This is what people mean by checking gold purity "with the number": the HUID is that number. In the BIS CARE app, choose "Verify HUID" and enter the six-character code. The app shows what was registered against that code. Since 8 June 2026, BIS has also recorded photographs and the weight of hallmarked gold articles, so a buyer can compare the piece in their hand with the record.
For a jeweller, showing a customer how to do this at the counter is one of the simplest ways to build trust.
Step 3: when there is no hallmark, test the metal
Old jewellery, gold taken in exchange, pieces from outside India and anything below the hallmarking thresholds may carry no hallmark. Then the gold has to be tested. The methods differ in what they tell you and whether they mark the piece:
| Method | Marks the piece? | What it tells you | Where it is used |
|---|---|---|---|
| XRF analyzer ("karat meter") | No | Gold content and the other metals in the alloy, at the surface | Jewellers, manufacturers, hallmarking centres, gold loan desks |
| Electronic karat tester | No | A karat reading only | Counters, old gold buying, field visits |
| Touchstone and acid | Leaves a streak on the stone and can mark the piece | An approximate karat, judged by eye | Traditional jewellers |
| Fire assay | Yes: a sample is taken and melted | The reference measurement of gold content | Assaying and Hallmarking Centres |
At a hallmarking centre, BIS guidelines put these in sequence: every article is screened by XRF first, then sampled and fire-assayed, and only then laser-marked. An article that XRF finds more than 5 parts per thousand below its declared fineness is returned without hallmarking.
What an XRF test can and cannot tell you
X-ray fluorescence is the method most jewellers mean when they talk about a gold testing machine or a karat meter. The piece sits in the instrument, X-rays excite the atoms in the metal, and the analyzer reads back which elements are present and in what proportion. It takes under a minute and leaves no mark, which is why it suits finished jewellery and walk-in customers. Our XRF explainer covers the physics and the published figures.
Its limit is that it reads the surface layer. A thick gold plating, or a surface that has been enriched in gold, can read higher than the metal underneath. That is not a fault of any one instrument. It is the reason hallmarking centres follow XRF with fire assay, and the reason to be cautious with unusual or heavy pieces offered as old gold.
Home tests: what they can and cannot do
Magnet, water-float, vinegar and bite tests circulate widely. At best they catch a crude fake: a strongly magnetic piece is not gold. None of them can tell 18K from 22K, and many common fakes pass all of them. If the purity matters enough to ask, it matters enough to check the HUID or have the piece tested.
For jewellers: when to own a gold testing machine
BIS does not require a jeweller to own a testing machine, so this is a business decision. The usual reasons to have one on the premises are:
- Buying old gold. Testing before you pay, and before you melt, protects the margin on every exchange.
- Checking lots before hallmarking. A lot that would fail the centre's 5 ppt XRF screen is cheaper to catch at your own counter.
- Controlling melts. Manufacturers test each melt so the alloy stays on grade.
- Gold loans. A quick, non-destructive reading at the desk.
For those jobs, compare our gold testing machines: the Signet FSDD and Signet Si-Pin benchtop XRF analyzers for the full alloy, and the portable electronic karat tester for counters and field visits. Where our online store publishes a price, the model page shows it.
Where to see and buy it
These are the Semsons Tech machines for this job. The store links let you book online; the other links open the full specifications or a quotation request.
| Machine and where to buy | Key facts |
|---|---|
| Signet FSDD XRF gold analyzer Buy or book on our store Full specifications | ±0.10% on gold, 1% to 99.99% Au Up to 72 elements, test in 10 to 60 seconds ₹18,99,000 incl. GST; book for ₹50,000 |
| Signet-PC XRF gold analyzer Buy or book on our store Full specifications | Benchtop XRF with a Si-PIN detector as standard Installation and operator training included ₹6,45,000 incl. GST; book for ₹50,000 |
| Portable gold testing machine Buy or book on our store Full specifications | Electronic karat tester (not XRF), shows 0 to 24K Battery powered, no mark on the piece ₹1,35,000 incl. GST |
Want to know which tester fits your counter? Send an enquiry or call +91 98216 12340.
Answers
Related questions
How can I check gold purity at home?
Read the hallmark and verify it. A hallmarked piece carries the BIS mark, a grade such as 22K916 and a six-character HUID, and you can check the HUID in the BIS CARE app. Home tricks with a magnet, water or vinegar cannot tell 18K from 22K. If a piece has no hallmark, take it to a jeweller with an XRF analyzer.
What does 916 mean on gold jewellery?
It is the fineness in parts per thousand: 916 means at least 916 parts of pure gold in every 1,000 parts of metal, which is 22 karat. The grade appears in the hallmark as 22K916. Other BIS grades include 18K750 and 14K585.
How do I verify a HUID?
Open the BIS CARE app, choose "Verify HUID" and enter the six-character code from the piece. Since 8 June 2026, BIS also records photographs and the weight of hallmarked gold articles, which the app can show.
Is a karat meter accurate?
It depends on the instrument. "Karat meter" usually means a benchtop XRF analyzer, and the accuracy is set by the model: our Signet FSDD is specified at ±0.10% on gold content. XRF reads the surface, so plated pieces can mislead it. A simple electronic karat tester gives the karat only.
Can gold plating fool an XRF test?
It can. XRF measures the surface layer of the metal, so a thick gold plating or a surface richer in gold than the core can read higher than the metal underneath. That is why hallmarking centres follow XRF screening with fire assay, and why a jeweller buying unusual or heavy pieces should be cautious about a single reading.