Assay / Assay Certificate
Also: assay card, bar certificate, certificate of assay, test certificate
An assay certificate is an authenticity document issued by an accredited testing body that formally confirms the fineness, weight and identity of a precious-metal bar.
An assay certificate (a certificate of assay, or simply an assay card) is a document issued by an independent, accredited testing body — or by the manufacturer itself — that is permanently linked to a precious-metal bar. It formally attests that the bar in question possesses the stated properties, in particular its fineness, gross weight, fine weight and serial number. For buyers, the certificate is the single most useful tool for authentication short of a full chemical analysis.
How an assay certificate comes about
Once a bar has been cast or minted, the refinery or a commissioned laboratory takes a material sample and analyses it. Common methods include:
- Fire assay (cupellation): the classic wet-chemical technique, treated as the reference method for gold and silver.
- X-ray fluorescence (XRF): contactless spectral analysis, fast and non-destructive.
- Flame atomic absorption (FAAS): a high-precision method for trace elements and alloy constituents.
The result is recorded on the certificate and tied to an individual serial number that is engraved or stamped on the bar.
Anatomy of an assay certificate
| Mandatory entry | Example |
|---|---|
| Manufacturer / testing body | PAMP Suisse, Heraeus, Valcambi |
| Bar number (serial number) | 00412857 |
| Metal | Gold (Au) |
| Gross weight | 31.103 g (1 troy ounce) |
| Fineness | 999.9/1000 |
| Fine weight | 31.100 g |
| Assay date | 2026-07-26 |
| Stamp / signature of the testing body | embossing or hologram |
Assay-card bars in a blister
The most common way to bind an assay certificate permanently to a bar is the so-called blister (also assay-card packaging): bar and certificate are sealed together inside a transparent plastic pack. As long as the blister is unopened and undamaged, the enclosed bar counts as certified and untouched. A broken or damaged blister usually lowers the dealer buy-back price, because the pairing of bar and certificate can no longer be proven beyond doubt.
Assay certificate versus LBMA Good Delivery
The LBMA Good Delivery label is not a single certificate for each bar, but an accreditation of the manufacturer and its production process. A Good Delivery bar (the 400-troy-ounce standard bar for institutional trading) does carry stamps with a serial number and fineness, but no accompanying assay card. The assay certificate as a physical companion document is chiefly relevant for small bars (1 g to 1 kg) in the retail segment.
Practical value on purchase and resale
When buying gold the assay certificate offers three concrete benefits:
- Instant authentication without your own test equipment — the serial number on the bar must match the certificate.
- Better resale terms — dealers usually accept certified bars in the original blister without a surcharge for re-testing; uncertified material is often bought at a discount to melt value.
- Documentation for estates and insurance — the certificate serves as proof of the bar's identity and value.
You can work out the melt value of a bar independently of the certificate at any time, based on the current gold price and the stated fine weight.
In brief
An assay certificate builds trust through demonstrable provenance: it ties a specific bar, via its serial number, to an independent test of fineness and weight. When buying small bars, keep the blister unopened to preserve the full documentation value. For tax or investment questions around resale, consult a specialist.