The headline difference
Solid gold is a gold alloy all the way through, from surface to core. A solid 18ct ring is 75% gold by weight whether you measure the outside, the inside, or the middle of the band. Gold-plated, gold-filled and rolled-gold pieces are a base metal core, usually brass, copper or silver, with a layer of gold on the outside. The thickness of that layer, and how it is bonded to the base, is what separates the categories.
For a charity shop the practical question is binary: solid gold goes in the postal pile; plated goes on the shop floor as costume jewellery. The rest of this guide is how to make that call quickly and confidently.
The markings to look for
| Marking | Meaning | Plate or solid? |
|---|---|---|
| 375, 585, 750, 916, 999 | Solid gold fineness stamp | Solid |
| 9ct, 14ct, 18ct, 22ct, 24ct | Solid gold carat stamp | Solid |
| GP | Gold-plated, thin electroplated layer | Plate |
| GEP | Gold electroplated | Plate |
| HGP | Heavy gold-plated | Plate |
| GF | Gold-filled, mechanically bonded sheet | Plate (thicker) |
| RGP | Rolled gold plate | Plate |
| 1/20 12K GF | 1/20th of weight is 12ct gold; rest base | Plate |
| 1/10 14K GF | 1/10th of weight is 14ct gold; rest base | Plate |
| EPNS | Electroplated nickel silver (silver-plate) | Plate (silver category) |
| "Gold tone" / "gold colour" | Marketing term, no gold content | Plate or no gold at all |
| 18KGP, 14KGP | 18ct / 14ct gold-plated | Plate |
| 18KP | Plumb gold, solid 18ct (US convention) | Solid (rare in UK) |
The convention is simple: a fineness number on its own (375, 585, 750, 916) is solid. The same number with letters after it (GP, GF, RGP, KGP, KGF) is plated. The presence of a fraction at the start (1/20, 1/10) is a giveaway for gold-filled, because the fraction is telling you the weight ratio.
Where plating wears through first
Plating is a coating, and coatings wear. On a piece that has been worn for years, the wear shows where the friction is highest. Look at:
- The high points of a ring shank, especially the part that rubs against the next finger
- The clasp of a chain or bracelet, particularly the catch and the spring mechanism
- The back of a watch case where it sits against the wrist
- The edges of a signet ring, where it has caught on door handles and pockets
- The earring posts, where they go through the ear
- The pin and catch of a brooch
On a worn plated piece, you will see a different colour breaking through the gold: a pinkish copper, a yellow-grey brass, or a bright white silver. That colour change is a definitive sign of plating. A solid gold piece will not show a different colour at worn edges, only the same alloy with more or less polish.
Weight and thickness physics
Gold is dense, about 19.3 grams per cubic centimetre for pure gold. Brass and copper, the most common base metals for plating, are about 8.7 and 8.96 grams per cubic centimetre. So a solid 18ct gold ring feels noticeably heavier in the hand than an identically-shaped 18KGP ring made from a brass core. The difference is not subtle: it is roughly twice the weight.
Weight on its own is not a definitive test, because some plated pieces are deliberately heavy (Victorian and Edwardian pieces especially), and some solid gold pieces are very light (modern hollow chains, fine wedding bands). Weight is one signal among several. Use it together with the markings, the wear pattern and the donor history.
The magnet test, and why it is not definitive
A common volunteer test is to bring a small neodymium magnet near a piece of jewellery. Pure gold, sterling silver and platinum are not magnetic. A piece that pulls strongly towards the magnet has an iron or steel content and is not solid precious metal.
The reason it is not definitive: plenty of plated pieces use brass or copper cores, which are also non-magnetic. So a piece that fails the magnet test (i.e. sticks) is not solid precious metal, but a piece that passes (i.e. does not stick) could still be plated brass. Treat the magnet as a quick rule-out, not a confirmation.
The charity-shop decision rule
For a volunteer sorting donations at speed, the rule that works is short.
- 1. Look for a number-only fineness stamp. 375, 585, 750, 916 or 999. Number on its own, no letters after. If present, set aside for posting.
- 2. Look for letter-codes that mean plate. GP, GF, RGP, KGP, KGF, 1/20, 1/10, EPNS. If present, the piece is plate and goes on the shop floor.
- 3. Look at the worn edges. If a different colour metal shows through, the piece is plate.
- 4. Pick it up. If it feels heavy for its size and there is a number-only stamp, it is solid. If it feels light or hollow and only has letter-codes, it is plate.
- 5. Send a photo if you are stuck. WhatsApp 07375 071158 with a close-up of the marks gets a same-day indicative read.
Plated pieces still have shop-floor value
Putting a plated piece on the shop floor is not a downgrade, it is the right place for it. Vintage costume jewellery in good condition is a genuine seller, especially named brands (Trifari, Monet, Sarah Coventry, Napier in the US; Mizpah, Exquisite, Attwood & Sawyer in the UK). A volunteer who knows how to read plating marks can price these pieces with confidence, and the postal pile stays clean of items that do not pay against the gold market.
Posting a sack of plated jewellery to a metal buyer wastes a parcel and disappoints the shop. Photographing the marks first, sorting on the table, and only sending the solid pieces is the practice that produces a clean monthly figure for the head-office report.
When the marks are missing or the piece is borderline
Some pieces sit in the grey area: no clear marks, plausible weight, donor history says "my mother said it was real". The honest answer is that no shop-table test will settle it. Send a clear photo on WhatsApp before deciding. We will give an indicative read on the marks and the surface, and if it still looks borderline you can post it for XRF assay under the standard process. Postal cover is up to £2,500, higher available on request before posting, and any item the charity chooses not to sell comes back free, tracked and insured. Indicative figures move with the market; the firm offer is set only after XRF assay confirms purity and weight of the specific items sent.
Watch cases and pocket watches: a special case
Donated watches deserve a moment of their own. A solid gold pocket-watch case from the late nineteenth or early twentieth century can carry a clear UK hallmark on the inside of the back cover, and the case alone may be worth a meaningful sum on metal content. The same shape of case in 9ct rolled-gold plate, marked "RGP" or "Dennison's patent", is plated and will not pay against the gold market.
For wristwatches, branded vintage pieces (Rolex, Omega, Cartier, Patek Philippe, Jaeger-LeCoultre, IWC and others) often have value as watches rather than as metal, and should be photographed in full and discussed before any metal-only routing. A piece sent in to GoldPaid that is recognised as a collectable watch will be routed for specialist valuation against auction comparables, not assessed as scrap. The trustee briefing sets out how non-bullion items are priced.
Coins, sovereigns and small bullion
Gold sovereigns and half-sovereigns from any year are solid 22ct gold (916 fineness). They are usually unmarked apart from the design itself, which is the legal tender mark. A donated sovereign in any condition, mounted or unmounted, is worth setting aside. Krugerrands, modern Britannias, Canadian Maples and American Eagles are stamped with their weight and fineness on the face. Small gold bars are usually stamped with the refiner name, the weight and "999.9".
A donated coin or bar should not be polished or cleaned before posting. Polishing can damage collectable value, and the surface condition does not affect the XRF reading.
Common questions
A ring is stamped "1/20 12K GF". Is that any gold at all?
A small amount. 1/20 12K GF means 1/20th of the total weight is 12ct gold, the rest is base metal. It is gold-filled, not solid gold, and is best placed on the shop floor as vintage costume jewellery.
What does 18KGP mean?
18 carat gold-plated. A thin layer of 18ct gold electroplated onto a base-metal core. It is plate, not solid, regardless of how good it looks.
A piece has no markings. Could it still be solid gold?
Yes, occasionally. Older pieces, foreign pieces, and items below the UK hallmarking weight threshold can be solid without a stamp. Send a photo first and we will give an honest read.
Will a chemical "acid test" damage the piece?
A traditional acid test files a small notch in the piece to expose the inner metal. XRF is non-destructive and does not need to file, scratch or mark the piece in any way.
A piece passes the magnet test. Does that prove it is solid gold?
No. The magnet test only rules out iron and steel content. Plenty of plated pieces with brass or copper cores will also pass the magnet test. The marks, weight and worn edges together give a better signal.
A donor insists their plated piece is "real gold". How do we explain it?
It often is real gold, on the outside. The plating layer is gold; the core is a different metal. The piece may still have great sentimental value and good shop-floor value as vintage costume jewellery.
Can we send a mixed bag of solid and plated for sorting?
It is much more efficient to sort on the table first using the markings and the wear test. If you have a borderline batch, send photos on WhatsApp before posting and we will guide you.