Almost every bad jewellery purchase comes from the same place: the listing gave a number, and the buyer assumed it meant something it did not. This is the whole of what you need to read one properly.
Everything else is decoration. A listing that does not give you these three is not a listing, it is a photograph with a price on it.
| Number | Why it decides |
|---|---|
| Net metal weight | Gross weight includes the stones, and stones weigh a lot less than gold. A 12 g "gold ring with diamonds" can hold 5 g of gold. |
| Purity | 18k is 75% gold, 14k is 58.5%, 9k is 37.5%. The same 5 g is worth twice as much in 18k as in 9k. |
| Stone weight and quality | Carat weight alone tells you almost nothing. A 1 ct diamond ranges from about €700 to about €12,000 depending on the other three Cs. |
| Mark | Meaning |
|---|---|
| 750 / 18K | 75% gold |
| 585 / 14K | 58.5% gold |
| 375 / 9K | 37.5% gold |
| 925 | Sterling silver |
| 950 / PT950 | Platinum, 95% |
A hallmark is a claim, not a guarantee. In the EU it is usually reliable; from outside it often is not. The words that mean there is no meaningful gold in the piece: gold plated, gold filled, rolled gold, vermeil, gold tone, gold coloured. Vermeil is silver with a gold layer, so it is worth the silver, and silver is worth roughly one eightieth of gold by weight.
"Tested as gold" or "acid tested" means someone scratched the surface. Plating passes that test.
Carat is weight, not size, and it is the least informative of the four on its own.
| C | What moves the price |
|---|---|
| Carat | Price per carat rises faster than weight: a 1.00 ct is worth far more than two 0.50 ct. |
| Colour | D to Z. D-F is colourless and expensive; G-J looks white in a ring; below N the yellow is visible. |
| Clarity | FL to I3. VS and up is clean to the eye. SI2 and below is where you must look at a photo. |
| Cut | The only C a human chose. A poor cut kills the sparkle whatever the other three say. |
Lab-grown stones are chemically identical to mined ones and sell for roughly 10% to 20% of the natural price, and that gap keeps widening. A listing that says "diamond" without saying "natural" in a market where lab-grown is everywhere is a question you must ask, not an assumption you may make.
Certificates. GIA, IGI and HRD are laboratory reports on that specific stone. An "appraisal", a "valuation certificate" or an "insurance value" is a number written by the seller or by someone the seller paid. They are not the same species of document, and the second one is worth nothing to you.
Rubies, sapphires and emeralds are routinely treated, and treatment collapses the value. The words to look for, because a careful seller does use them: heated, glass-filled, lead-glass, fracture-filled, diffusion, dyed, composite, reconstituted.
A 3 ct untreated Burmese ruby is a serious stone. A 3 ct lead-glass-filled ruby is worth less than the gold around it, and both are called "3 ct ruby" in a listing.
The same applies to the word "gemstone" used vaguely. If nobody names the species, assume the cheapest one that fits the photo.
The hammer price is not the price. On a €1,000 hammer at a typical platform, buying inside the EU:
| Line | Typical |
|---|---|
| Hammer | €1,000 |
| Buyer's premium (9% to 25%) | +€90 to €250 |
| VAT on the premium | +21% of that |
| Shipping and insurance | +€15 to €60 |
| From outside the EU: import VAT on the total, plus duty | +21% and up |
A lot bought outside the EU commonly lands 35% to 45% above the hammer price. That is the number to compare against the value, and it is the reason a lot that looks cheap often is not.
A seller who answers all five plainly is usually a seller worth buying from. One who answers none has told you something too.
The same piece is honestly worth five different numbers, and which one applies depends on who you are and what you are about to do.
| Rung | What it is |
|---|---|
| Intrinsic | Melt the metal, break out the stones. The floor. Nothing sells below it for long. |
| Wholesale | What a dealer pays, knowing they must resell it. |
| Fair price | What a private sale between two informed people looks like. This is the number you should aim at. |
| Second-hand shop | What a shop charges, having paid wholesale and added rent and risk. |
| New retail | A new piece with a brand on it, in a shop. The top rung, and the one every listing quotes at you. |
The gap between the floor and the top rung pays for the setting, the design, the brand, the shop and the risk. Nothing about it is illegitimate. The point is knowing how big it is before you agree to pay it.
Free, no account: metal at today's live price, stones at wholesale, and the whole ladder.
Now put a piece through the calculator