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<p>[QUOTE=&quot;desertgem, post: 755758, member: 15199&quot;]I agree with Doug on the cotton cloth.</p><p><br /></p><p>Copper has hardness of 3, a young human nail about 2.5, gypsum 2, and talc 1.&nbsp; Take a new copper cent and rub it with talc or gypsum powder or &quot;mud&quot;, and you will find out for yourself, the surface will look different. Or take a nail cutting and &quot;scratch&quot; the end across the coin.</p><p><br /></p><p>When cotton fibers dehydrate and age they become more brittle and harder on the microscopic surface. Some of these &quot;microscopic surface tips&quot; can become like thorn tips.</p><p><br /></p><p>Hardness can vary significantly depending on the orientation of the atoms/molecules in a material. Diamond has a harness of 10, but in actuality, in a single stone, due to the arrangement of the carbon atoms in the crystal, will have&nbsp; a much greater hardness in a different direction. When diamonds are cut, either with cleaving or a diamond blade, the cutter has to determine the plane to cut the diamond, so they don&#039;t try to cut a harder layer with common diamond abrasive.</p><p><br /></p><p>So a cotton fiber can&#039;t penetrate into the copper, but it can abrade the surface of the metal.</p><p>IMO.</p><p><br /></p><p>Jim[/QUOTE]</p><p><br /></p>

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