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<p>[QUOTE=&quot;Publius2, post: 7807361, member: 105571&quot;]Spots on coins after using acetone followed by a water rinse can arise for several reasons:</p><p><br /></p><p>1)&nbsp; The acetone is not clean.&nbsp; You should only use fresh acetone from a newly opened container.&nbsp; Once used, discard that acetone and soak in another batch of fresh acetone.&nbsp; Discard that acetone.&nbsp; Some people like three soaks but two will usually perform adequately.&nbsp; DO NOT pour the used acetone back into the container of fresh acetone for the fresh acetone will then be irredeemably contaminated.&nbsp; This is a common source of spotting:&nbsp; When the contaminated acetone evaporates, it leaves behind whatever isn&#039;t acetone.&nbsp; And the contaminants don&#039;t only come from the coin but also the container you&#039;re soaking the coin in, your hands and/or gloves, and the atmosphere.</p><p><br /></p><p>2)&nbsp; If you rinse the coin in water, use distilled water.&nbsp; You can buy it at the grocery store for little to nothing.&nbsp; I recommend distilled water rather than demineralized water because commercial distilled water has little to no mineral salts in it.&nbsp; Commercial demineralized is basically just the product of an ion exchange process that &quot;soften&quot; the water by converting the hardness (measured as calcium carbonate) into other products.&nbsp; Although &quot;demineralized&quot; water is also sometimes the product of a reverse osmosis process that also removes mineral salts.&nbsp; But in neither case is the product as pure as distilled water.</p><p><br /></p><p>3)&nbsp; If you use a rinse water that contains anything but H2O, when that water evaporates it will leave the contaminants behind.&nbsp; That is the spotting you see on the coins.&nbsp; Now, some folks say if you dab the coin dry after rinsing with tap water or demineralized water, then you can avoid the spotting.&nbsp; I am not challenging that assertion.&nbsp; What I am saying is that for a coin of value, why would you take a chance to avoid the cost of a $2 gallon of distilled water from the grocery store?</p><p><br /></p><p>4)&nbsp; Water has been described as &quot;the universal solvent&quot; and indeed it is.&nbsp; And in the form of distilled water, it possesses even more of that ability to dissolve what it comes into contact with.&nbsp; For highly reactive metals like copper, a rinse in distilled water must be a fleeting contact.</p><p><br /></p><p>5)&nbsp; Finally, even after rinsing with distilled water, I agree with the advice to dab it dry as quickly as possible.&nbsp; As soon as the wet coin is exposed to the air, the water will start evaporating but not before it starts absorbing contaminants from the air, including dust and various aerosols.&nbsp; So, you want to remove the water before it can absorb contaminants which it would then leave behind even if dabbed dry later.</p><p><br /></p><p>6)&nbsp; And, of course, you want to keep your reagent chemicals (acetone and distilled water) closed up as much as possible so that they don&#039;t absorb stuff from the air.[/QUOTE]</p><p><br /></p>

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