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<p>[QUOTE=&quot;Rob Woodside, post: 7499574, member: 96187&quot;]On a more fundamental level: Is there any relative mtion between the metal and the die? Does the metal skid across the die to where it is needed? Or does the metal roll across the surface of the die to where it is needed once the metal contacts the die? </p><p><br /></p><p>In a skid there is relative motion between the two materials at their interface. Here that&#039;s the die and planchet. In a skid an asperity attached to the die would dig a groove in the planchet and an asperity in the planchet&#039;s surface would try to dig a groove in the much harder die. This could account for one off grooves on the coin and, eventually with enough wear, parallel grooves in the die that would produce&nbsp; parallel ridges on the coins. A one off scratch on a coin won&#039;t produce chatoyancy, but the die will eventually wear with many parallel scratches producing the observed chatoyancy.</p><p><br /></p><p>However we learn from fluid mechanics that in non turbulent flow the boundary layer of fluid around a static body is at rest with the body. It is hard to think of the short distance flow that fills the die as turbulent. So here the metal contacting the die stops still and the metal atoms away from the die surface then roll across one another to where they are needed. In this case the die would faithfully express its ridges as grooves and its grooves as ridges. This cannot account for the observed build up of parallel wear lines on the die that should produce riges on the coin giving it chatoyancy.</p><p><br /></p><p>Maybe a metallurgist could tell us whether metal skids or rolls as it fills a die on striking?[/QUOTE]</p><p><br /></p>

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