A Complete Guide To Cleaning and Preservation of Coins, page 20
HOW TO CLEAN LEAD, CLUSTERED and LACQUERED COINS: Methods and Applications
NOTE: All chemical cleaning methods are relatively safe. However, their use and application are entirely at the reader's risk. We assume no responsibility for damage to property or personal health.
HOW TO CLEAN LEAD COINS
Lead coins were minted in South Asia around the time of Christ and in the 19th century. Lead has often been used for counterfeit coinage because it appears as silver when new and casts well.
The following methods can be used for cleaning lead coins:
1) Degreasing Lead Coins can be accomplished in alcohol.
2) Immersion into Acetic Acid Solution: the lead coins are put in 10% Acetic acid (CH3COOH) and the coatings removed by treatment with soft brushes. After rinsing the coins are placed first in a 5% Ammonia solution and then in pure Alcohol. They are heated then somewhat over a spirit flame or on a hot plate and are brushed with a warm brush lightly dipped in paraffin, and the excess paraffin is rubbed off with a chamois cloth.
3) Sodium Hydroxide (Caustic Soda) Method: the lead coins are placed in sodium hydroxide with alcohol (methyl alcohol) added. After washing, the coins are heated in a solution of lead acetate containing free acetic acid, and then another washing is given.
4) Electrochemical Reduction with Zinc Dust and Acetic Acid: the coins are placed in zinc dust in a glass vessel and then acetic acid is poured over them. This electrochemical reduction method (described on page 15) is used when hard deposits are involved. The process must be watched continuously and the coins must be rotated.
HOW TO CLEAN CLUSTERED (UNEARTHED) COINS
Sometimes a newly dug coin cache consists of many coins firmly stuck to each other, or clustered. In Italy and North Africa they are called Unearthed Coins. It cannot be seen immediately what the condition of the eventually treated coins may be. Treatment of such coins usually requires considerable experience.
The following steps can be done for cleaning clustered coins:
1) Separation of Coins: An attempt is made first to separate the groups, freed from soft dirt by rinsing or brushing, into individual coins. If thin coins are not involved, this also can be done by striking with a wooden mallet or a rubber hammer.
2) Soaking: If the clusters cannot be separated in this manner, they are placed first in water for a few days, preferably distilled water, to which some dissolved baking soda can be added. The clumps must be moved continually.
If it is certain that silver or silver alloys are involved and not copper, bronze or brass, then the soaking can be done in water with a small addition of 2% Sulfuric acid (H2SO4).
CAUTION: DILUTION OF SULFURIC ACID MUST ALWAYS BE DONE BY POURING ACID INTO WATER IN A FINE STREAM, NEVER by pouring water into concentrated sulfuric acid!
3) Boiling: the coins then are boiled as follows, depending upon the coinage metal.
• Boiling Silver Coins: Silver coins are heated in the powdered Baking Soda. The soda powder is put into a crucible (porcelain container) and the coins are placed in it. During heating the coins are continually moved, every five minutes at first, and rinsed and brushed.
• Boiling Gold Coins: Baking Soda is dissolved beforehand in water, and the gold coins are boiled in it. This method is gentler than that for silver.
• Boiling Copper Coins: Copper coins are boiled in Sodium Hydroxide (Caustic Soda) dissolved in water beforehand. The coins are moved from time to time, then rinsed and brushed.
In every case the coins are thoroughly rinsed at the end and are soaked for half hour with frequent changes of water. After the coins are separated, all the cleaning methods under the individual treatments described above can be used.
CLEANING LACQUERED COINS
To preserve the transparency of the lacquer, lacquered coins may be cleaned only with fingers, carefully in a dilute soap solution. After cleaning, the coins are rinsed with lukewarm water, and then it is best to pat them dry carefully with a chamois cloth, avoiding all rubbing.
If the lacquer has worn spots, the coins must be delacquered by spirit alcohol (for Spirit Lacquer or Shellac-coated coins) or acetone (for Plexistol Lacquer) or benzene turpentine (for Black Japan) and lacquered anew (described on page 26).