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<p>[QUOTE=&quot;desertgem, post: 2043175, member: 15199&quot;]All of the substances mentioned above are equal or harder than coin metal if we are referring to a scratch test ( Moh&#039;s method). Silver and gold are between 2.5-3.0, and copper , brass, and bronze are 3 range. The average wood is usually listed as 3 also.&nbsp; You can tell by taking a coin and see if the edge will produce a scratch when moved down the wood piece and then reverse and see if the wood edge would scratch the metal coin. Don&#039;t do this if the appearance of the coin afterwards matters to you. A piece of human fingernail is about 2.5. The thorns mentioned go from 2.5-3+ depending on how old they are. Measurement of Mohs hardness is mainly for minerals, so there is little data on organic substances. Interesting is that rice hulls can measure up to 5 as they have silicates in their structure <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie1" alt=":)" unselectable="on" unselectable="on" /></p><p><br /></p><p>Even microscopic scratches can affect the surface appearance as to grade luster. Also consider that the gunk accumulates in certain areas/densities and to remove any may reveal underlying changes that easily show the coin as altered surfaces.[/QUOTE]</p><p><br /></p>

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