XRF vs Fire Assay in the Numismatic Profession

My last article pointed out that industry shifts in the numismatics industry (as a result of counterfeiting) point to an increasing need for highly sophisticated analytical technologies to verify the precious metal content of numismatics.

Examining the overall presentation of the coin with a loupe or magnifying glass, noting the mint year, surface alterations, special marks, and visible damages will help decide about the general condition and authenticity. Ping tests, electrical conductivity devices, and acid tests have played a role in determining precious metal content and karat value but they all have their limitations. With the rise of fake coins being found in the marketplace, better analysis is needed.

“Fire assay” is the oldest known method of assaying gold and is very accurate. However, the gold must be destroyed/melted down to be analyzed. That’s the last thing you want to happen to your collectible coins, so you should stay away from that method.

XRF Can Be Used to Determine the Chemical Composition of Materials

A widely used technology — that is non-destructive — for analyzing and verifying precious metal content is X-ray fluorescence (XRF). X-ray fluorescence (XRF) is an analytical technique used to determine the chemical composition of materials.

XRF occurs when a fluorescent (or secondary) x-ray is emitted from a sample that is being excited by a primary x-ray source. These x-rays are typically emitted from a miniaturized x-ray tube. Each of the elements present in a sample produces a unique set of characteristic x-rays that is a “fingerprint” for that specific element. XRF analyzers determine the chemistry of a sample by measuring the spectrum of the characteristic x-ray emitted by the different elements in the sample when it is illuminated by x-rays. Because this fluorescence is unique to the elemental composition of the sample, XRF is an excellent technology for qualitative and quantitative analysis of the material composition.

XRF quickly provides the exact percentages of all elements within an item – easily identifying non-standard, under-karated, and even sophisticated counterfeit precious metals that acid testing is incapable of differentiating.

XRF vs Fire Assay Results

We recently tested some samples to find the gold content. Here is a comparison of XRF to fire assay. As you can see by the chart below, XRF analysis shows a very high correlation with the fire assay method. And most importantly, XRF analyzers won’t destroy the coin.

To get more information about these methods and results, including how X-ray fluorescence (XRF) can aid in assessing the value of collectible coins, read the Adding Value to the Numismatic Profession application note.