Spanish hallmarking: what the assay mark guarantees
The assay mark certifies that an authorised laboratory has verified that the precious metal content matches the declared fineness, and it is applied alongside the fineness mark and the responsibility mark of the maker or importer.
gelisted editorial team · Updated 15 August 2026
The short version
- Three distinct marks: fineness, responsibility and assay.
- X-ray fluorescence testing costs 15 € to 40 €.
- Older and imported pieces may carry no Spanish mark.
- Declaring a higher fineness than the real one is a consumer offence.
Three separate marks fit inside a 2 millimetre band, and each answers a different question about the piece.
The three marks
The fineness mark states the pure metal content in parts per thousand: 750, 585, 925. The responsibility mark identifies the maker or importer who declares that fineness and stands behind it. The assay mark certifies that an authorised laboratory has verified the content by test. Together they convert a commercial claim into a checked fact.
| Mark | Applied by | What it certifies |
|---|---|---|
| Fineness mark | maker | declared parts per thousand |
| Responsibility mark | maker or importer | who stands behind it |
| Assay mark | authorised laboratory | verification by test |
| X-ray fluorescence test | laboratory or jeweller | 15 to 40 € |
| Cupellation test | laboratory | destructive, most precise |
| Older pieces | often unmarked | assay required |
| Imported pieces | mark of origin | may be valid |
When there is no mark at all
It does not mean the piece is false. Jewellery made before marking became general, older handmade work and many inherited items carry none. Marks are also lost when a ring is resized several times, since the stamp usually sits inside the band and disappears when the shank is cut and rejoined. In those cases the only route is an assay, and the non-destructive version leaves the piece untouched.
The two test methods
X-ray fluorescence analyses the surface without damaging the piece, in 30 to 90 seconds and for 15 € to 40 €. Its limitation is that it reads the outer layer, so a plated item can give a misleading result unless it is combined with a density check. Cupellation is destructive, requires a sample of material and is the reference method in disputes, costing 40 € to 120 €.
For a private sale, fluorescence plus a density calculation settles almost every case.
If the fineness does not match
Selling a piece as a higher fineness than it actually is is a consumer offence and gives the buyer the right to unwind the sale and recover the price. With an invoice, an assay report and a written complaint, the seller's response period is limited and the consumer route usually resolves the matter without escalation. Keeping the descriptive invoice, with fineness and weight itemised, is what makes that possible.
Frequently asked
+What does the assay mark certify?
That an authorised laboratory has verified by test that the content matches the declared fineness.
+Is an unmarked piece false?
No. Older, handmade and resized pieces frequently carry no mark.
+How can fineness be checked without damage?
By X-ray fluorescence, which reads the surface in under two minutes for 15 € to 40 €.
+Is that method always reliable?
Not on plated pieces, since it reads the outer layer. It should be combined with a density check.
+What if the fineness is lower than sold?
It is a consumer offence and, with invoice and assay report, the sale can be unwound.
Sources
- 1Boletín Oficial del Estado, BOE (August 2026)
- 2London Bullion Market Association, LBMA (August 2026)