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Message:: [QUOTE="TypeCoin971793, post: 2425131, member: 78244"]I doubt that there would be much difference between machines and a patinated or unpatinated coin. Now completely crusty coins are a different story, but I have not tried using an XRF on these. To understand why I think this, one needs to understad how XRF machines work. They emit X-Rays (the first two letters of XRF) into the target metal. These X-Rays excite the electrons in the atoms in the coin as they absorb energy from the radiation. When the electrons revert to a more-stable, lower-energy state, they emit photons equal to the drop in energy. The atoms in each element have specific absorption and emission energies, called atomic spectra. The XRF machine measures the relative intensity of the spectra and outputs a ratio of atoms present. The accuracy of the measurement depends on the precision of the device, which is why the better ones are more expensive. As each type of atom has a specific atomic spectra, I would think that different machines should be able to record the same relative intensities of atomic emission and absorbtion spectra, meaning the recorded ratios of elements present should be the same. The precision of the machine might affect this if the values of the specific spectra of two elements are very close to one another. The patina is usually thin enough to represent only a small percentage of the atoms present, so it can be ignored.[/QUOTE]