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<p>[QUOTE=&quot;RonSanderson, post: 3257522, member: 77413&quot;]I&#039;m not sure if this is the same mechanism as the bubbles that plague the early copper-zinc business strikes.</p><p><br /></p><p>I believed those were better characterized as bubbles if they were separations of the copper cladding from the underlying zinc. I do wonder what was in those bubbles, or if the metals merely separated and created a small chamber of near-vacuum between the layers - namely, the bubble could not contain any air unless it was punctured.</p><p><br /></p><p>On these proofs, I don&#039;t feel like the layers have separated. (Disclaimer, I don&#039;t know anything about metallurgy.) I would speculate that these were ripples caused by differences in the rate of plastic deformation during striking due to the different densities and metallic crystalline structures of thin-film copper (I&#039;ve heard it&#039;s about 20 microns thick) and the much thicker core of zinc underneath.</p><p><br /></p><p>Is there a metallurgist on the forum? I&#039;d really like to know!</p><p><br /></p><p>Here&#039;s a 1982 Zincoln. To me these look like bubbles, where the proof looks like waviness or ripples.</p><p>[ATTACH=full]856158[/ATTACH][/QUOTE]</p><p><br /></p>

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