A Complete Guide To Cleaning and Preservation of Coins, page 18
HOW TO CLEAN ALUMINUM & IRON COINS: Effective Methods & Applications
NOTE: All chemical and electrical 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 ALUMINUM COINS and TOKENS
Since aluminum coins and tokens have been in circulation only for a short time in numismatic history, they are scarcely collected in other than mint state. On these coins and tokens oxidation occurs extremely easily or they show traces of retention in collections.
Chemical treatment is hardly feasible as aluminum is one of the coinage metals that is attacked even by Sodium Hydroxide (Caustic Soda). It is therefore advisable to protect aluminum from oxidation by lacquering (described on page 26).
The following methods can be used for cleaning aluminum coins and tokens:
1) Immersion into a Hydrogen Peroxide (H2O2) Bath, described on page 11, applied briefly.
2) Removing Aluminum Tarnish: a proven method is that of first steeping coins or tokens in hot soapy water, followed by rapid drying by patting, and then polishing with a high speed glass brush in a drill press or lathe. A cloth pressed against the brush in the rotating machine will clean it.
HOW TO CLEAN IRON COINS
Because of the iron's susceptibility to rust, iron was not used as a coin metal until recently. For example, the US 1943 zinc-coated steel cents were produced as emergency money due to the war demand for copper.
To protect iron coins against corrosion, various coatings such as copper, brass, nickel and zinc have been used. And even with use of coatings, iron coins have been mostly used as emergency money.
Most of the iron coins of different compositions actually have a steel rather than iron core. Steel represents iron alloys containing small levels of carbon.
The following methods can be used for cleaning iron coins:
1) Removing Iron Rust. Rust is not difficult to remove. It can be done by:
• Immersion into Petroleum Oil and, after a few hours, rubbing them off with a cloth. This is not a pleasant method because of the odor of the petroleum oil.
• Rubbing with Cloth and Vitrinol Copper Soap (or similar agent). If the result is not as complete as expected, the coins can be placed for a short time, perhaps ten minutes, in copper soap paste and then rubbed.
They are then rinsed off and briefly neutralized in a solution of Baking soda and Caustic soda, and again rinsed. Drying is done as quickly as possible with a hot air blower or by immersion in Acetone.
• Using Rust Removal Paste, available in hardware stores. Instructions for use are given by the manufacturer.
• Immersion into Coca Cola Classic for an hour or longer.
2) Electrochemical Reduction with Zinc and Sodium Hydroxide (Caustic Soda): the Electrochemical Reduction method is described on page 15 and is done according to the electromotive series (see a table on page 15). The iron coins are laid between zinc chips, over which 5% sodium hydroxide is added; it must completely cover the zinc. The coins should not touch one another.
The galvanic current formed between metals dissolves the iron oxides, which precipitate on the zinc as zinc oxides, or go into solution. From time to time, the coins must be removed, rinsed and brushed. If the treatment lasts for a long time, zinc must be added. Several hours of soaking with frequent changes of water follow.
3) Alternating Treatment: The iron coins first are immersed briefly in 10 % Ammonia solution. A short bath in dilute Sulfuric acid then follows and then a bath in ammonia solution to remove the black discoloration. Finally, after rinsing, the coins must be rubbed with prepared chalk.
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!
4) Immersion into Hydrochloric Acid Solution: The rusty iron coins are cleaned in Hydrochloric acid, 10 % to concentrated, by immersion, for 10 to 30 minutes. After brief rinsing, a brief neutralization with 10 % Ammonia solution follows.
5) Mechanical Treatment: The coatings often are not completely removed or discoloration may occur. The coins must be given a subsequent mechanical treatment, and this is possible because iron is very hard. The first stage of treatment consists of rubbing with a glass brush.
A better method is to mount the glass brush in a lathe or drill press. In the absence of a drill press, iron coins also can be worked on with 000 steel wool; the effect is often amazing. Iron coins that have a dark protective film should be touched only with a glass brush, to prevent harm to the protective film.
As in any chemical treatment, iron coins should not remain unwatched, for example, overnight, in a solution. The iron involved rarely is pure; it always contains traces of copper, manganese, sulfur or tin, which can lead to discoloration in lengthy treatment.
The progress of a treatment must be checked continuously because the time duration may be different.
The coins are taken out with acid-resistant tongs (or two pieces of wood), rinsed and rubbed with a hard brush.
Soaking and Drying of Iron Coins: A simple rinsing after treatment is not enough for the iron coins. They must be rinsed carefully as described in section "Soaking" on page 6, so that no residues of chemicals will remain on the coins and be able to cause subsequent discoloration. Drying of iron coins is of equal importance.
At first, they are always dried with a cloth or blotter, and then most easily with hot air blower, or the coins also may be placed on a hot (about 140 °F (60 °C)) oven or hot plate. An electric cooking plate also can be used. Iron coins also can be dried by immersion in Acetone or Alcohol (spirit, methyl alcohol).
It is important to protect basically and initially all iron coins by lacquering, so that rust damage cannot occur. Mint state iron coins cannot be salvaged after a severe rust attack. The very thin coating of iron coins with Kerosene is to be recommended. This film dries in a short time.
If you would like to recommend this article to everyone, please click the button: