Both marks are honest — nobody is lying by stamping something “gold filled” or “gold plated” rather than solid gold. The confusion is that the two sound like variations on the same idea, when in the US they are separately defined terms with different legal minimums a mile apart in what they guarantee.
The rule that separates them
US jewellery marking is governed by the FTC’s Guides for the Jewelry, Precious Metals, and Pewter Industries, at 16 CFR Part 23. Section 23.3 sets out what each term is allowed to mean, and the difference comes down to how the layer of real gold is measured.
Gold plate, gold plated, and rolled gold plate require a mechanically bonded layer of at least 10 karat gold making up at least 1/40th of the total metal weight of the piece.
Gold filled requires the same mechanical bonding and the same 10 karat floor, but at at least 1/20th of the total weight — twice as much gold, by the same method of measuring it. That factor of two is the entire legal difference between the two terms, and it is also the practical one: a gold-filled layer is thick enough to survive decades of normal wear, where a 1/40th plating layer is not.
A third category, gold electroplate, is measured differently again — not as a fraction of weight but as an actual thickness, at least 10 karat and at least 0.175 microns of fine gold. Push that thickness to at least 2.5 microns and the piece may be marked heavy gold electroplate (HGE) — thicker than ordinary electroplate, but a mechanical bonding process rather than electroplating is still what produces the far heavier gold-filled layer.
Why gold filled and gold plated do not last the same
A gold-filled layer is bonded under heat and pressure, and there is simply more of it — at minimum, twice the weight fraction that plating requires, and in practice most commercial gold-filled stock runs to 1/20th or 1/10th, well above the legal floor. It can be polished, lightly buffed, and worn daily for decades before wearing through, which is why pre-1980s gold-filled jewellery still turns up in good condition today.
Plating and electroplate layers are, by definition, far thinner — an electroplate layer sits at a small fraction of even the legal gold-filled minimum. They wear through at points of friction: the underside of a ring shank, the edge of a clasp, the high points of a chain link. Once through, the base metal underneath shows, and there is no bringing the layer back short of re-plating.
What neither is worth as scrap
The gold in a gold-filled piece is real and calculable — this site’s gold filled value calculator works it out directly from the fraction stamped on the piece. It is also, in almost every case, not worth a refiner’s time: separating a thin bonded layer from its base metal costs more in chemistry than the recovered gold is worth, so refiners decline gold-filled scrap outright. Plated and electroplated pieces carry even less gold and are declined for the same reason, more emphatically. Both hold their value as jewellery — much gold-filled work is well made and wears for decades — rather than as bullion.
The full list of what every common stamp claims, gold and otherwise, is in the hallmark reference.