How pure is pure? | Canvas of Knowledge

A number needs a representative sample

An assay determines the composition of material submitted for analysis. That immediately creates a second question: does the analysed sample represent the larger item? LBMA places sampling and assaying together because a highly precise laboratory result is useful only when the sample is suitable. In a bar containing different materials or an uneven composition, examining one location cannot simply establish every other location. The quality of the conclusion depends on the relationship between sample, method and object. [1]

Fire assay examines a taken sample

Fire assay is a long-established laboratory method used to determine precious-metal content. It separates and measures precious metal from a prepared sample, rather than reading the outward appearance of a finished bar. LBMA identifies it as a reliable technique in the refining industry. Taking material for analysis can damage or alter the original object, so the method answers a different practical need from a quick non-destructive screening test. This article describes that distinction without providing a home-testing procedure. [1]

X-rays reveal the surface

X-ray fluorescence, usually abbreviated to XRF, identifies elements from their characteristic response to X-rays. It can provide a rapid reading without cutting into the tested surface. The important limitation is depth: LBMA explains that these instruments primarily examine the outermost layer. Plating can therefore conceal a different interior. A result consistent with high-purity gold at the surface is useful information, but it must not be presented as an unconditional verdict on the entire object beneath it. [3]

Evidence comes in layers

Other tests answer other questions. Ultrasound, for example, can help detect internal irregularities, but LBMA does not describe it as a measurement of fineness. Its physical-market guidance rejects the idea of one definitive non-destructive solution for every bar. Reliable assessment combines an appropriate method with sampling, records and the chain through which the metal has passed. A convincing screen display is the beginning of an interpretation; understanding what the instrument actually measures completes it. [2]

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Sources & further reading

Sources checked 14 November 2026. The artwork is illustrative. Reference organisations do not endorse this website. Financial examples are educational, not investment recommendations.