Cleaning and Preservation of Coins - A Complete Guide
CHEMICAL CLEANING OF COINS BY ELECTROLYSIS
4) Electrolysis Concept and Design
Electrolysis is the chemical decomposition of suitable materials by direct electric current. This method of cleaning can be very effective on coins that do not respond to other cleaning methods. An example would be silver coins oxidized from long-term submersion in water. Copper and nickel coins can be cleaned using electrolysis also, but their patinas will be removed.
You can make a simple electrolysis cleaner with a few household items and inexpensive parts:
1) an AC/DC converter or an adapter from any old household device such as a transistor radio or a telephone base capable of 400-700mA (milliampere) output
2) two "alligator" clips of the solderless type with the screw clamp for the
wire (they can be purchased from your local electronics or hardware store)
3) a medium size glass or porcelain container
4) a stainless steel spoon or fork to be used as an electrode
5) common table salt solution as an electrolyte
Attach one clip to each of the two wires from the converter. If you know which wire is the positive lead, mark it as such. If the alligator clips came with colored rubber boots, slide the red one over the positive (+) wire/clip assembly.
Partly submerge the spoon upright in the glass container and clamp it to one side of the container using the positive (+) (anode) alligator clip. Place the edge of the coin to be cleaned in the jaws of the negative (-) (cathode) alligator clip.
NOTE: Be aware that the alligator clip may put marks into the coin's surface. A good metal to metal contact is required for the process to work properly.
Submerge the coin in the saltwater solution (electrolyte) to the tip of the alligator clip. DO NOT TOUCH THE SPOON WITH THE COIN! Plug the converter into a AC wall outlet, the solution around the coin will start to bubble. Dirt and oxidation will immediately leave the coin and darken the electrolyte solution.
If this reaction does not take place, it is probably because you were unsure of the output wire polarity or your converter is simply not functioning. Swap clips on the spoon and coin and try again. NEVER TOUCH THE CLIPS TOGETHER, ALWAYS UNPLUG THE CONVERTER FROM THE WALL OUTLET FIRST!
NOTE: Do not use a high electric current, which will
peel metal off the coin.
NOTE: Do not use the same bath for silver, copper
and nickel coins.
If you do not want to destroy the coin, you need to watch the effects of electrolysis on the coin's surface, and regulate the time the coin is in the electrolyte solution. If left in too long, the surface of the coin will start to get pitted, and the coin will start to deteriorate.
Below is an example of the pitted surface of a US 1812 War button that has been left in for a little bit too long.
Below is a picture of two buttons placed next to each other for comparison: a button on the left was uncarefully cleaned by electrolysis, the button on the right was cleaned by brushing after being soaked in olive oil for two days.
5) Soaking After Cleaning
When coins are soaked, the following rules must be observed:
A. After a chemical treatment coins should be soaked about a half-hour.
B. The coins never should lie still for long periods in tap water or even distilled water because chemical residues on the coins or deposits on the bottom of the vessel can cause attacks which may be evidenced as discoloration.
C. The coins never should lie on top of each other, because this can cause precipitation from the
action of galvanic current, described in "Reduction" on page 14. This is certainly true for coins
of different metals, and may be true also for coins of apparently similar metal,
but of different alloys.
For instance, if several silver coins lying partly one on top of the other are allowed to stand in tap water for a long while, "Shadow Images" will form almost certainly.
D. Coins of different metals should not be soaked together, and the water should be changed every 10 minutes, turning over the coins at the same time. The tap water might be considerably contaminated with substances that can become active during the soaking, therefore the distilled water is preferable.
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