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