To Clean or Not To Clean
By Dr. Sol Taylor
When, then, is it OK to clean a coin, and how is it to be done properly?
If a coin is caked with dirt, grease and such when found in the ground or in a pile of nails or household items, the cleaning procedure is as follows.
First, determine if the coin has some numismatic value. If it is a common silver coin (1964 and earlier) and shows signs of wear, use whatever silver cleaning compound you have at home and you will get a nice, shiny coin. It is still worth only the silver content, known as "junk" silver.
If the coin appears to be in mint condition that is, has Mint sheen under the grit or shows luster around the rim and is not an ordinary junk silver coin, use a dip such as JewelLuster. Follow the instructions on the jar, and be sure to rinse it in distilled water or pure alcohol when finished with the dip. That will remove the grit and most of the tarnish. If you're lucky, the coin will look a lot better than before, and maybe even close to uncirculated.
This is a risky process which requires an experienced eye, a delicate touch, a good sense of timing, and an element of luck. Many such dipped coins look artificial and as such are worth less than if left alone.
Never use anything abrasive on potentially valuable coins such as steel wool, a toothbrush, silver polish or special cleaning cloths.
Do not attempt to conceal a bad cleaning job by putting the coin in the oven to tone the surface, which may hide some blemishes. Some such techniques include baking a coin inside a potato for 35 to 45 minutes at 350 degrees, or heating a coin in ketchup for 10 minutes at 300 degrees. There are many "recipes" for the artificial toning of a coin.
If the coin is gold, a quick dip in a mild acid such a household bleach, muriatic (pool) acid or even nitric acid will remove surface grime, finger marks, and even toning although gold coins usually do not show toning. Hold the coin with tongs by the edges and rinse thoroughly in alcohol to dry.
Old copper coins (pre-1857) require more intensive work to restore whatever quality features lie beneath the layers of dirt, grime, tarnish and oxides. The obvious excess can be carefully removed with a toothpick or air brush.
The nature of the surface will determine which chemicals and tools are best suited for the job. Carbon spots are the hardest to remove but can be lightened with a dab of Nic-A-Lene or CCC applied with a toothpick or tiny pipette. Oxides and carbonates, usually in the form of greenish crust, can be removed with a light application of a weak acid or Nic-A-Lene; the underlying surface may have been pitted as a result of the enrustation.
The restoration of a copper- or bronze-colored surface can be achieved with a very careful application of miniscule amounts of highly toxic compounds of cyanide, mercury oxide or similar products. No one should try these even in a laboratory with an exhaust hood, proper tools and safety backups.
Bronze coins (post 1864) require similar treatments and often do well with a quick dip of Nic-A-Lene or CCC. Heavily encrusted, darkened coins will look just as bad after cleaning, as the removed areas will be pitted, eroded and often discolored. For coins that are submitted for encapsulation by the major grading services, many (or most) cleaned coins are returned ungraded.
Cleaning coins that have been immersed in sea water for long periods require overnight bathing in diluted muriatic acid to remove the lime encrustation. This may also leave pitting on the surface, but the coins generally will appear better than before. Many treasure ship coins have been so treated and look "salty" as a result of being cleaned for resale. Many have also been carefully brushed to get deeper into the lime deposits.
This is not the process for any other types of coins that need a cleanup. Many ancient coins have also undergone this type of cleaning to better identify the features.
From 1975 to 1977, I conducted several laboratory sessions at the American Numismatic Association's Summer Seminars where students worked on cleaning coins that needed some attention. The end result of several days of careful cleaning and restoration was that about half the coins came out better looking than before, while the other half came out worse off than before.
For the beginner, the answer to whether to clean a coin is generally NO.
Numismatic Guaranty Corp. offers professional "restoration" services for more valuable coins that need a little "makeover" at the hands of professionals. Such treatment also tends to add points to the coins' eventual grades.
Dr. Sol Taylor of Sherman Oaks is president of the Society of Lincoln Cent Collectors and author of The Standard Guide to the Lincoln Cent. Click here for ordering information.
©2008 SCV COMMUNICATIONS GROUP & SOL TAYLOR · ALL RIGHTS RESERVED.