Karat, fineness and assay results explained, and why a purity figure only means something when it is attached to a documented test of identified material.
Karat and fineness describe the same thing differently
Karat expresses how much of an alloy is gold in twenty-fourths. Fineness expresses the same proportion in parts per thousand and is the unit used in professional bullion trade, because it carries more precision and fewer rounding conventions.
As a reference: 24K is approximately 99.9% gold (999.9 fine), 22K approximately 91.6% (916), 18K is 75% (750) and 14K approximately 58.5% (585). These are conversions, not measurements. Converting a number does not verify it.
A claim is not evidence
Colour, density in the hand, stamping, a photograph or a seller's description are not evidence of composition. They are indications at best, and each of them can be reproduced by material that is not what it appears to be.
Evidence is a documented determination performed on identified material by an identified party using a stated method on a stated date. The distance between 'this is 99.9% gold' and 'this lot, identified as X, was assayed on this date by this laboratory using this method, returning this result' is the entire difference between a marketing claim and a product specification.
What a usable assay report contains
A usable report identifies the material it applies to, states gross and fine weight, states the fineness determined, names the method used, gives the date and identifies the party who performed the analysis.
If any of those elements is missing, the figure cannot be traced back to a specific piece of material and should be treated as unverified, however confidently it is presented.
Methods differ, and the difference matters
Fire assay is a destructive method regarded as the reference technique for determining gold content. X-ray fluorescence is non-destructive and fast, but it reads a surface rather than a volume, which is why it is used for screening and confirmation rather than as a final determination on heterogeneous material.
Neither method is universally correct. Which is appropriate depends on the material, the transaction structure and what the parties have agreed, which is why the method is recorded rather than assumed.
Why sampling decides the result
An assay reports on the sample it received. If the sample does not represent the lot, the result is accurate and useless at the same time. This is why sampling procedure, conditions and the retention of counter-samples are treated as part of the verification process rather than as preliminaries to it.
Sources and references
- — OECD Due Diligence Guidance for Responsible Supply Chains of Minerals from Conflict-Affected and High-Risk Areas
- — General assaying practice; specific figures in any transaction come from the assay report issued for that material
This article is general market and educational information. It is not investment, legal, tax or financial advice, and it is not a commercial offer. No prices or indicative values are published on this website; commercial terms are discussed directly with qualified counterparties.
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