XRF testing for silver and gold.

How it works

X-ray fluorescence (XRF) aims a beam of X-rays at the metal. Each element gives off X-rays at its own characteristic energies, so the analyzer can tell which metals are present and in what proportions: for example 92.5% silver and 7.5% copper in sterling. Handheld and benchtop models are both common.

It reads only the surface

The signal comes from a thin surface layer, from a micron or two to a few tens of microns deep, depending on the metal. That makes XRF excellent for identifying an alloy, and weak against fakes built in layers:

• Plated pieces: silver plating over base metal can read as silver.
• Filled bars and coins: a core of another metal under a silver shell isn't seen.
• Surface changes: old silver coins can have a silver-rich surface that reads finer than the coin really is.

How dealers use it

XRF is non-destructive and fast, so it's used to check purity and catch plated or wrong-alloy pieces. For bullion, it's paired with weight, dimensions, and a through-the-metal test such as a Sigma verifier. The LBMA says no non-destructive method, XRF included, can replace a destructive assay for certain results.

Sources

• Science Education Resource Center, Carleton College, X-ray fluorescence (XRF).
• Ager et al., combining XRF and GRT for the analysis of ancient silver coins (analysis depth and surface enrichment).
• LBMA, Good Delivery rules and governance.

Silver tests: How to test silver · Specific gravity · XRF · Sigma verifier · Magnet · Acid · Ice · Ping · Is my silver real? · Silver stamps

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