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<p>[QUOTE=&quot;-jeffB, post: 4602298, member: 27832&quot;]Oh, they&#039;re <i>fantastic</i> tools. But they read from a relatively thick layer of the surface (even on gold), over a pretty wide area of the surface.</p><p><br /></p><p>So, maybe that spot is all copper and copper oxides. But that&#039;s a layer a few hundred nanometers thick. The XRF gun is reading to a depth of maybe 10 microns, 10,000 nanometers. It&#039;s also reading over a spot size of maybe a centimeter, possibly as small as 3mm across if you have the expensive kind. So <i>most</i> of what it will be reading is pure bulk gold, and the spot&#039;s composition will be so &quot;diluted&quot; by that surrounding gold that it&#039;ll be very hard to read.</p><p><br /></p><p>All my speculation, of course, as I don&#039;t have an XRF gun or a selection of spotted .999 gold coins on hand. But I don&#039;t see how it could work any other way.[/QUOTE]</p><p><br /></p>

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