Cleaning Silver Coins - Tutorial, page 3
Simple & Quick Method for Brightening Silver Coins of Silver Content Higher than 0.203
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NOTE 1 - Preventing Appearance of Pure Copper on Coins of Low Silver Content:
Always make sure you have enough of lemon acid solution in the container with coins. This may be important if you are treating silver coins of low silver content, and they have other admixtures besides copper in their alloys. Copper content is evidenced by appearance of copper sulfate encrustation on dug coins' surfaces.
During the process of dissolving copper salts, the products of chemical reactions are copper citrate, oxygen and carbon dioxide. While the bubbles of oxygen and carbon dioxide leave the solution, the copper citrate stays in the solution; thus, its concentration is increasing. As copper salts get dissolved, the concentration of copper citrate reaches a certain high point.
If the immersed silver coin has a low silver content, with zinc present in the coin metal (a rare case in silver coins but still a possibility), the following is more likely to happen. As the fast disappearing copper salts expose more and more copper, copper citrate begins to react with zinc in the alloy.
Because zinc is more active than copper, a redox (oxidation and reduction) chemical reaction begins. As a result of this reaction, pure copper begins to appear in form of pink crystals at the spots where copper sulfate was present not long ago. These pink fissured stains certainly make the coin unattractive.
Unlike the silver coins, the copper coins are more likely to be damaged by this process when they are immersed into the lemon-acid solution. To avoid this problem, a large amount of solution is used, and the solution should be changed a few times during the process.
4) Brush Your Coin with a Toothbrush and Toothpaste
Now it is important to clean the gray-bluish substance off the coins' surface. This substance is the combined product of chemical reactions between Lemon Acid and Silver Tarnish, and between Lemon Acid and copper salts. Brushing with toothpaste effectively gets the job done, followed by rinsing with water.
Brushing a Silver Wire Hammered Coin with Toothpaste
After the coins are rinsed with water and dried with napkins or cloth, they are ready to be displayed.
A Silver 1583 ½ Öre Coin Has Been Cleaned
If there are still some dark spots of tarnish, like a dark spot at 10 o'clock on the coin's obverse shown on a picture above, remaining on the coin after cleaning with this method, use the most effective Electrochemical Reduction Cleaning Method for Tarnished Silver Coins to remove them.
NOTE 2 - Preservation of Silver Coins:
As silver is tarnished by hydrogen sulfide (gaseous) in the air, silver coins will turn dull again over time, usually within a month, if not protected. To avoid their tarnishing, you can either keep the coins in cellophane or polyvinyl chloride bags or to cover them with oils that are especially designed for preserving coins. If such oil (sold in any coin collector's shop) is not readily available, you can "shield" your coin with mineral or olive oils (you can find more information on preservation of coins useful Tips for Cleaning Coins).
Ideally, you should keep your silver coins in a low-humidity environment. You can place a small bag of activated charcoal or a piece of chalk in your "coin-drawer" to minimize future tarnish. If you do not want to bother with preserving your silver coins, their appearance can be easily restored by rubbing them with a soft eraser.
If you would like to learn other effective methods for cleaning silver coins, please visit Other Methods for Cleaning Silver Coins.
To learn my simple and effective method for cleaning copper coins, please visit Effective Method for Cleaning Copper Coins.
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