How to Identify Authentic Gold and Diamond Items

Key takeaway: Identify authentic gold by its hallmark, weight and density, and a magnet or acid test. Verify diamonds with the 4 Cs, a jeweller’s loupe and a thermal tester. When real money is at stake, have items checked by a trusted exchange.

Most people who own gold and diamonds have no real way of knowing what they hold until the day they decide to sell. An inherited ring, a coin tucked away for years, a watch bought on a trip abroad: each carries a story, but the story does not tell you whether the metal is solid 18 carat or a clever plated copy. Learning to read the signs yourself puts you in a far stronger position, whether you are buying, insuring or selling.

At The Gold Avenue in Illovo, Sandton, we test gold, coins, diamonds and luxury watches every working day. This guide walks you through the same checks a professional dealer uses, in plain language, so you can recognise the real thing and spot the fakes before they cost you.

Reading Gold Hallmarks and Purity Marks

The fastest way to gauge a piece of gold is to find its hallmark. Pure gold is 24 carat, but it is too soft to wear, so jewellery is almost always alloyed. In South Africa you will commonly see 9ct, 14ct, 18ct and 22ct pieces, while Krugerrands and many investment coins carry their own distinct stamps.

Look for a small stamp on the inside of a ring band, the clasp of a chain, or the back of a pendant. These are the marks worth knowing:

• 375 means 37.5 percent gold, or 9 carat.
• 585 means 58.5 percent gold, or 14 carat.
• 750 means 75 percent gold, or 18 carat.
• 916 or 917 means 91.6 percent gold, or 22 carat.

A genuine hallmark is crisp and evenly struck. Be cautious of marks that look smudged, shallow or hand-scratched. Two stamps to treat as warnings rather than reassurance are GF (gold-filled) and GP (gold-plated). Both mean a thin layer of gold over a base metal, not solid gold throughout.

Assessing Weight and Density

Gold is a remarkably heavy metal, denser than almost anything it is faked with. A genuine gold item feels substantial in the hand, heavier than its size suggests. A coin or chain that feels suspiciously light for its bulk deserves a closer look.

Density is also the principle behind the water test. Solid gold sinks quickly and decisively because it is so dense. A piece that floats, hesitates or drifts down slowly is likely hollow or made largely of a lighter base metal. This is a rough indicator rather than proof, but combined with the hallmark it tells you a great deal.

Simple Gold Tests You Can Try

A few low-cost checks will catch the more obvious fakes before you ever reach a dealer.

• Magnet test. Gold is not magnetic. If a strong magnet pulls at your item, there is a magnetic base metal inside it. Note that a non-magnetic result does not prove gold on its own, since some fakes use non-magnetic metals too.
• Acid test. Jewellers apply testing acids matched to specific carat levels. Real gold of the stated purity resists the acid, while plated or lower-grade pieces discolour. This is best left to someone experienced, as the acids are corrosive.
• Skin and wear test. Plated items often wear through at edges and high-contact points, showing a different colour underneath. Green or dark marks left on the skin point to a base metal beneath a thin gold layer.

None of these is conclusive on its own. A dealer reaches a confident verdict by combining the hallmark, the weight, the acid result and electronic testing.

Judging a Diamond by the 4 Cs

Diamonds are graded on four characteristics, known across the trade as the 4 Cs. Understanding them helps you tell a fine stone from an ordinary one, and a real diamond from a simulant.

Cut

Cut refers to how well the stone is shaped and faceted, which governs how it handles light. A well-cut diamond returns bright flashes of light. A dull stone that seems to leak light from the bottom may be poorly cut or may not be a diamond at all.

Colour

Diamond colour is graded from D, which is completely colourless, down towards Z, which carries a visible yellow or brown tint. The closer to colourless, the rarer and more valuable the stone, all else being equal.

Clarity

Clarity describes the tiny internal features, called inclusions, and surface marks. Grades run from Flawless down through various Included categories. Natural diamonds almost always carry some inclusions. A stone that looks utterly perfect at a bargain price should make you suspicious.

Carat

Carat is weight, not size, with one carat equal to 200 milligrams. Two stones of the same carat weight can look quite different depending on how they are cut.

Tools for Inspecting Diamonds

A few instruments separate genuine diamonds from glass, cubic zirconia and moissanite.

• Jeweller’s loupe. A 10x loupe reveals natural inclusions, facet sharpness and the small imperfections that real diamonds carry. Simulants often look too clean or show rounded, worn facet edges.
• Thermal tester. A handheld diamond tester measures how the stone conducts heat. Diamonds conduct heat in a way most simulants cannot match, though moissanite can fool basic testers, which is why dealers use combined instruments.
• UV light. Many diamonds fluoresce under ultraviolet light. The reaction varies from stone to stone, so it is a supporting clue rather than a single deciding test.

Common Signs of a Fake or Low-Grade Item

Whether you are looking at gold or diamonds, a handful of red flags should slow you down:

• Flaking, peeling or worn patches that reveal a different metal underneath.
• Stamps reading GF or GP, or no hallmark at all on a piece sold as solid gold.
• A diamond that looks flawless yet is offered far below what a real stone of that size would cost.
• Damaged or filed-down serial numbers on luxury watches and coins.
• Paperwork that does not match the item, or a certificate from a body you cannot verify.

Why a Professional Valuation Still Matters

Home tests are useful for catching obvious fakes, but they have limits. A magnet cannot tell solid gold from a non-magnetic plated piece, and a basic tester can be misled by moissanite. When the value of an item runs into real money, the safe move is to have it examined properly.

At The Gold Avenue, we weigh and test every item in front of you, explain what we find, and price gold against the live spot price along with the condition of the piece. There is no obligation, no pressure and no hidden deductions. We built the business in Illovo as a transparent, five-star alternative to the traditional pawn-and-gold trade in Johannesburg, and our international dealer network, particularly in the UAE, lets us pay local sellers more competitively. If you are selling, remember that proceeds may have tax implications, and SARS treats certain sales accordingly, so keep your records.

Sell or Verify Your Gold and Diamonds in Illovo

If you would like a clear, honest assessment of your gold, diamonds, coins or luxury watch, our team in Sandton is ready to help. Our process is simple:

1. Contact us by phone, WhatsApp or online chat.
2. Book a valuation at our Illovo premises.
3. Receive an offer once your items are weighed, tested and priced on the live market price and condition.
4. Get paid the same day by cash or EFT.

The Gold Avenue
Illovo Point, 68 Melville Road, Illovo, Sandton, 2196
Phone: 010 109 0080
WhatsApp: 076 393 5429

Frequently Asked Questions

Can I tell if gold is real at home?

You can catch obvious fakes at home using the hallmark, the weight, a magnet test and the water test. These checks are helpful, but they do not match a professional acid and electronic test, so confirm anything valuable with a dealer before you rely on it.

What does 750 stamped on gold mean?

A 750 stamp means the item is 75 percent gold, which is 18 carat. Similarly, 585 is 14 carat and 375 is 9 carat. A GF or GP stamp, by contrast, means gold-filled or gold-plated rather than solid gold.

How do I know if a diamond is real and not cubic zirconia?

Look through a 10x loupe for natural inclusions and sharp facets, then check the stone with a thermal diamond tester. Real diamonds conduct heat differently to most simulants. Because moissanite can fool basic testers, a dealer uses combined instruments for certainty.

Do you buy gold and diamonds in Johannesburg?

Yes. The Gold Avenue buys Krugerrands, gold coins, gold and diamond jewellery and luxury watches from the public at our premises in Illovo, Sandton. Items are weighed and tested in front of you, priced on the live market, and paid out the same day by cash or EFT.

Learn More

At The Gold Avenue, we simplify the process of selling your valuable assets. From luxury watches and Krugerrands to gold, diamond jewellery, and more, we offer fast, safe, and convenient buying services, coupled with an enjoyable experience. We stand by our promise to provide the best price for your items.

Krugerrands: Sell your Krugerrands swiftly and securely.

Gold Jewellery: Turn your gold jewellery into instant cash.

Gold Coins: Get the best price for your gold coins.

Diamonds: Exchange your diamonds for a competitive price.

Watches: Luxury watches like Rolex and others are welcome.

In need of a cash loan? We’ve got you covered.

Selling to The Gold Avenue is simple:

Contact Our Team: Reach out to our team via call, WhatsApp, or online chat. Describe the luxury items you want to sell.

Book an Appointment: Set a valuation appointment at a time convenient to you. Our safe and secure premises are located in Johannesburg.

Get an Offer: Our expert team will provide a quick and fair valuation. We’re committed to long-term relationships, guaranteeing the best price.

Money in Your Bank: We offer immediate payments, directly into your bank account, either through cash or EFT.

Ready to start selling? Book an Appointment