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<p>[QUOTE=&quot;Conder101, post: 290577, member: 66&quot;]If the coin is laying flat in the acid, as it eats the metal bubbles of hydrogen are formed that come up from underneath.&nbsp; They tend to rise up along the edge in the same place each time&nbsp; so the edge is etched slightly unevenly and this can create the ribbed look around the edge of the coin.</p><p><br /></p><p>Another possible reason for the ribbing on the edge is that when the blank is punched from the strip there are definite vertical lines created by the shearing action.&nbsp; when the edge of the coin is milled the hardness of the coin will still vary very slightly in the pattern of those shear lines.&nbsp; This varying hardness can also result in a slightly different reate of attack on the metal by the acid.[/QUOTE]</p><p><br /></p>

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