The vocabulary
| Term | Meaning |
|---|---|
| Fineness | Gold content expressed in parts per thousand — 995.0 means 99.5% gold. |
| Karat | Gold content in twenty-fourths. 24K is nominally pure; 22K is 916 fineness. |
| Gross weight | Total weight of the item as presented. |
| Net or fine weight | The weight of contained gold: gross weight multiplied by fineness. |
| Outturn | The refinery's determination of recoverable fine metal after processing — the figure that usually governs final settlement. |
| Doré | Semi-pure alloy from mining or initial processing, requiring refining to reach investment fineness. |
The methods
Fire assay (cupellation)
A sample is fused, the base metals oxidised and absorbed into a cupel, and the remaining precious metal bead weighed. It is destructive, takes hours, requires a properly equipped laboratory, and it is the reference method — the one refineries and courts rely on. Because it consumes and measures the whole sample rather than a surface, it cannot be defeated by plating or a foreign core.
X-ray fluorescence (XRF)
A handheld or benchtop instrument reads the elemental composition of the surface layer, in seconds, without damaging the item. It is genuinely useful for screening large numbers of items and for confirming that a refined bar is roughly what it claims to be. Its limitation is fundamental rather than a matter of instrument quality: it reads microns deep. A tungsten core under a gold skin reads as gold.
Specific gravity
Weighing in air and in water gives density. Gold is unusually dense at 19.3 g/cm³, so most substitutes fail immediately. Tungsten is the exception at almost exactly the same density, which is precisely why it is the fraudster's metal of choice — so specific gravity alone is not sufficient either.
Ultrasonic testing
Measuring the speed of sound through a bar detects internal discontinuities and cores. It pairs well with XRF and specific gravity because it addresses exactly the gap they leave, and it is non-destructive.
What to write into the contract
- The named laboratory, and who instructs and pays it.
- The sampling protocol, and who is present at sampling and weighing.
- Whether settlement follows origin assay or destination outturn.
- The tolerance between assays that triggers a dispute, and the umpire laboratory whose result is final.
- How retained samples are held, by whom, and for how long.
- How weights are established and reconciled, and on whose calibrated scales.
For refined metal moving into the international market, the London Bullion Market Association's Good Delivery framework sets the recognised standard for bars and the refiners accredited to produce them. Where a buyer needs metal that will be accepted without re-refining, the practical route is material refined by an accredited refiner rather than material assayed at origin.