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<p>[QUOTE=&quot;Oldhoopster, post: 5360963, member: 84179&quot;]The sigma machine measures the resistivity of the metal and compares it to a standard for the alloy.&nbsp; Indian (beginning midway through 1864) and Lincoln cents are 95% copper 5% tin and zinc.&nbsp; Since the ratio of tin and zinc can vary, the actual alloy can vary.&nbsp; You need to know if a variable tin/zinc ratio changes the resistivity to the point where Sigma can&#039;t develop a standard baseline.&nbsp; Or maybe, there are no detectable differences </p><p><br /></p><p>A couple other things to consider</p><ul> <li>What kind of planchet will be used for a counterfeit?&nbsp; 100% copper is easily available.&nbsp; Is there detectable resistivity difference between 95% Cu and 100% Cu. Assuming Sigma can develop a baseline standard, will they be able to tell the difference?&nbsp; I wouldn&#039;t worry about alloys with more Sn and Zn, since you&#039;ll start seeing color change</li> <li>Laminations are known to occur in Cooper cents, and that will affect the resistivity</li> <li>&quot;Woody&quot; cents (improperly mixed alloys) may generate false readings</li> </ul><p>I&#039;m not a metallurgist, and don&#039;t know if any of these are significant, but any/all of them could be a reason why Sigma doesn&#039;t offer a setting for copper cents.&nbsp; I recall reading in their literature that their equipment may give false readings on early US coinage due to allowing methods used at the time (don&#039;t hold me to that as I&#039;m going from memory)[/QUOTE]</p><p><br /></p>

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