The short answer
Gold filled jewellery has a thick layer of karat gold mechanically bonded — with heat and pressure — to a base-metal core, usually brass. Gold plated jewellery has a far thinner film of gold deposited on the surface, usually by electroplating. The difference in the amount of gold is enormous: a gold filled layer can be many times thicker than a typical plated one.
How gold filled is made
A sheet or tube of karat gold is bonded to a core of brass or copper, then rolled or drawn down to size. Because the gold is a solid layer rather than a coating, it wears slowly and can last for generations with normal use. That’s why a 1920s pocket watch chain marked 1/20 12K GF can still look bright today.
Under US trade guidelines — which most gold filled makers followed — “gold filled” means the karat gold layer is at least 1/20 of the item’s total metal weight, and at least 10 karat. The mark tells you both numbers: in 1/20 12K GF, the layer is 1/20 of the weight and is 12 karat gold.
How gold plating works
Electroplating deposits gold from a solution onto the surface of a finished piece. Standard plating is measured in microns — thousandths of a millimetre — and is often well under one micron thick. Even “heavy” electroplate (marked HGE) is only a few microns. Plating can look beautiful when new, but it wears through on edges and clasps, and there is very little gold to recover.
Reading the marks
| Mark | What it usually means |
|---|---|
| GF, G.F., 1/20 12K GF, 1/10 10K GF | Gold filled — a bonded layer of at least 1/20 of the weight |
| RGP, 1/40 12K RGP | Rolled gold plate — a bonded layer, thinner than gold filled |
| RG, R.G., Rolled Gold | Rolled gold — bonded construction, layer often not stated |
| HGP, HGE | Heavy gold plate / heavy gold electroplate — thicker than standard plating, varies by maker |
| GP, GEP, 18K GP, 18K GE | Gold plated or electroplated — usually too thin to recover |
A mark like “18K GP” catches a lot of people out: the 18K describes the colour or purity of the plating, not the item. It is not 18 karat gold.
Checks you can do at home
- Find the mark. Look on clasps, jump rings, inside ring bands, on watch case backs and on the bail of lockets. A loupe or your phone camera’s zoom helps.
- Look at the wear. Plated pieces often show a different-coloured metal on high points and edges. Gold filled tends to wear evenly and slowly.
- Try a magnet. Gold filled is built on brass, which isn’t magnetic. If a strong magnet grabs the body of a piece (not the clasp spring), it’s likely plated steel.
- Don’t scratch or acid test. Home acid kits can give misleading results on layered metals and can damage collectible pieces.
Why it matters when you sell
Because gold filled carries a real layer of karat gold, it has recoverable value — especially in quantity. Plated jewellery usually doesn’t. Our gold filled calculator shows roughly how much pure gold a piece contains from its weight and mark, and the Will we buy it? checker tells you straight away whether a mark is one we buy.