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<p>[QUOTE=&quot;-jeffB, post: 25245481, member: 27832&quot;]I think of the Sigmas as electromagnetic testers. (Really, <i>all</i> of the things you listed are precious metal verifiers, aren&#039;t they? <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie2" alt=";)" unselectable="on" unselectable="on" />)</p><p><br /></p><p>Moderately thick gold plating over <i>anything</i> will fool an XRF. Gold plating over tungsten will fool specific gravity, weight, and magnet. But I don&#039;t know of any approach that will fool an electromagnetic test <i>and</i> one of the others simultaneously -- gold and tungsten have different conductivity and magnetic susceptibility, and the frequencies used in Sigma-type testers will reach more than deep enough to scan an entire coin or bar.</p><p><br /></p><p>I suspect an acoustic test would be difficult to fake, too, but I don&#039;t like people thwacking my coins, and I wouldn&#039;t trust their ears anyhow, and I don&#039;t know of any commercial testers that use acoustics.[/QUOTE]</p><p><br /></p>

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