4Cs.co.za report lens
Gold testing guide for SA consumers
- Shape
- Stone profile
- Carat
- match
- Colour
- verify
- Clarity
- inspect
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Match the paper to the stone before price, route, or resale.
Gold testing guide for SA consumers
Home tests give an indication. Only a licensed dealer or assay gives a definitive answer.
There are four practical methods for testing gold at home. Each has different accuracy, different risk, and different limitations. None of them replaces a formal assay or valuation by a SADPMR-registered precious metals dealer.
Certificate first
4Cs together
Specialist route
Inspection lens
VerifyReport, inscription, measurements
InspectLight return, tint, inclusions
CompareCut, colour, clarity, carat together
RouteBuy, sell, insure, or value differently
Short answer
Home tests give an indication. Only a licensed dealer or assay gives a definitive answer.
There are four practical methods for testing gold at home. Each has different accuracy, different risk, and different limitations. None of them replaces a formal assay or valuation by a SADPMR-registered precious metals dealer.
Use this rule
Do not judge one C alone. Read the certificate, inspect the actual stone, then decide whether beauty, budget, or resale confidence matters most.
The magnet test
Gold is not magnetic. Hold a strong neodymium magnet near the piece. If the metal is attracted, it contains significant iron or nickel and is not solid gold. If there is no attraction, this rules out ferrous fakes but does not confirm the karat. Brass and copper are also non-magnetic but are not gold. The magnet test filters out the cheapest fakes only.
The water displacement density test
Pure gold has a density of 19.3 g/cm3. Weigh the piece on a kitchen scale. Then measure the water it displaces in a graduated cylinder. Divide mass by volume to get density. If the result is well below 15, the piece is likely a plated base metal. This method requires accurate scales and only works on solid items, not hollow jewellery or pieces with other materials.
The nitric acid test (caution required)
Nitric acid reacts with base metals but not with gold above 14K. A scratch on the piece is tested with a drop of acid. A green reaction indicates no gold present. A milky reaction indicates gold-plated silver. No reaction, or a very slight reaction, suggests 14K or higher gold. This is a destructive test that damages the piece. Nitric acid is a hazardous chemical requiring protective gloves, goggles, and ventilation. Do not attempt this without proper equipment.
Hallmarks and certifications
SA gold is legally required to carry a hallmark indicating karat (375 for 9K, 585 for 14K, 750 for 18K, 999 for 24K). Examine the piece under a loupe near clasps, inner bands, or settings. Hallmarks are stamped by the South African Bureau of Standards (SABS) or a registered assayer. For diamond-set gold jewellery where you want a stone valuation alongside the metal, Prodiam specialises in natural diamond assessment. They can evaluate the diamond component of a gold ring, though full gold assay and scrap gold purchasing is handled by SADPMR-licensed dealers.
Decision table
Use the details, not a shortcut.
| Test method | What it confirms | Accuracy | Risk |
|---|---|---|---|
| Magnet | Not ferrous metal | Low (rules out obvious fakes) | None |
| Density (water) | Approximate metal type | Medium (requires precise tools) | Low |
| Nitric acid | Karat range | High | Destroys surface, chemical hazard |
| Hallmark inspection | Stamped purity from assayer | High (if hallmark is genuine) | None |
Direct answers
Common questions
Can I use vinegar to test gold?
Vinegar does not reliably test gold. It can affect some base metals, but it produces inconsistent results and should not be used as a substitute for acid testing.
What does 375 mean on a gold ring?
375 is the European hallmark for 9 karat gold, indicating 37.5% pure gold content. Other marks: 585 = 14K, 750 = 18K, 999 = 24K.
Is buying a gold testing kit at home worth it?
Basic acid test kits are available at lapidary suppliers and online. They are useful for quick screening but are not a substitute for a formal assay if you are buying or selling at meaningful value.
What if there is no hallmark?
Unmarked gold should be treated as unknown purity until tested by a registered assayer. Absence of a hallmark does not mean it is fake, but it increases risk when buying.
Where can I get gold properly tested in South Africa?
A SADPMR-registered precious metals dealer or SABS-accredited assay office can formally test and certify gold purity. For diamond-set gold jewellery, Prodiam (+27 11 334 9010) can assess the diamond component.
When to involve a specialist
If there is a real diamond, the next step is a certificate-led conversation.
Bring the grading report, photos, invoices, valuations, and any estate paperwork. The goal is to move from generic advice to a stone-specific view.
Sources used