01Decisive
Read the fraction in the stamp
'1/20 18K GF' means one twentieth of the weight is 18 karat gold and the rest is brass. The fraction is the whole disclosure and it is often the smallest part of the mark. A loupe is needed on worn pieces.
750 · Lovenhall Ring
The 18K GF (Gold Filled) Mark
A bonded layer of real 18k over base metal, far thicker than plating and far less than solid.
The millesimal mark for 18 karat gold, used worldwide3 references
Gold filled is a mechanically bonded sandwich: a sheet of karat gold pressure-welded to a brass core, then worked as one metal. In the United States the standard requires that the gold layer be at least one twentieth of the total weight for the piece to be called gold filled, which is why the mark is usually written as a fraction — 1/20 18K GF means 5 percent of the weight is 18 karat gold.
That makes it a genuinely durable product. The layer is perhaps a hundred times thicker than electroplating, and good gold-filled jewellery can be worn for decades without wearing through, which is why it dominated affordable jewellery for most of the twentieth century.
It is still not solid gold. It cannot be sized or repaired like solid gold because heat and filing breach the layer, and it has essentially no scrap value because recovering 5 percent gold from a brass matrix is not economic. Rolled gold plate, marked RGP, is the same idea with a thinner layer and a lower legal threshold.
References and sizes
18K GF · 1/20 18K GF · 18K RGP (rolled gold plate)
Establish which of these you are holding before judging it. A genuine piece read against another reference's rules will look wrong when it is not.
Model-specific checks
What decides a 18K GF (Gold Filled)
These apply to this model and not to the rest of 750. Work them alongside the maker's general checks, not instead of them.
02Strong
Check the edges and the inside of a shank
Gold filled wears through eventually, and it goes at the sharpest edges and the highest points first, revealing yellow-pink brass. Because the layer is thick, wear-through often appears as a small window rather than a broad patch.
03Supporting
Expect a jeweller to decline to size it
Gold filled cannot be sized or soldered like solid gold without breaching the layer. A jeweller refusing to resize a ring stamped 18K GF is telling you what it is.
The market
What a 18K GF (Gold Filled) does on the secondary market
Above plated, well below solid. Effectively no recoverable gold value.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Questions we are asked
- Is gold filled real gold?
- The layer is real karat gold, and it is far thicker than plating — US rules require at least one twentieth of the total weight, which is why the stamp reads like 1/20 18K GF. But the core is brass, so the piece is not solid gold, it cannot usually be sized or repaired, and it has essentially no scrap value.
- What is the difference between gold filled and gold plated?
- Thickness and method. Gold filled is a sheet of karat gold mechanically bonded to a brass core, at least 5 percent of the total weight, and it can last decades. Gold plated is an electrodeposited layer measured in microns or fractions of one, and it wears through in months to a few years.
All the 750 checks
Free tools of the room
Lovenhall RingRead the whole piece
The mark tells you what the metal claims to be. The instrument reads the setting and the stones together and gives a range to orient you — before anyone charges you for an appraisal.
Free on iPhone & iPad. An estimate, never an appraisal.
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