From time to time every coin enthusiast needs to clean silver coins. Silver coins that are several centuries or millennia old and that were stored in less than ideal conditions often come with heavy cement-like, grey, black, or deep blue deposits. The deposits can be very thick if the coins were buried in the ground for long, as is often the case.

These coins can be cleaned with electrolysis or through immersion in an acid bath, but both of these methods remove silver from the coins if not controlled properly. The best method to clean without attacking the coin is known as Autoelectrolysis. The method is gentle and it only removes the deposits, not the silver itself.

Autoelectrolysis: Electrolysis is the name of the procedure when two dissimilar metals are immersed in an acidic or alkaline solution and when electricity is passed through them from an external battery. Autoelectrolysis on the other hand has two dissimilar metals and an acidic or alkaline bath, but no external battery. Whatever electricity passes through this system is self-generated, and is only of the order or milli or micro amperes and does not harm coins.

The Apparatus: Making an autoelectrolysis system for cleaning silver coins is very easy. You need some aluminum sheets, silver coins, and some lemon juice. The silver coin needs to be placed in contact with aluminum and it is to be covered with lemon juice. A chemical reaction sets in soon with or without a fizz depending upon a number of factors. The coin can be cleaned of the deposits after the reaction and the electric current loosens the deposits.

The time needed to loosen the deposits may vary from 30 minutes to 30 hours. Coins that need more than 6 hours should be brushed clean after every six to eight hours and fresh lemon juice should be poured to allow the reaction to start all over again.The aluminum sheet might also need a change if most of it has been consumed.

Since a coin-collector keeps on cleaning silver coins, household aluminum vessels are not suitable for the job. They become coated with chemicals after four or five sessions of cleaning and the vessel is no longer useful for anything. The best method is to use aluminum vessels or sheets that can be disposed after one or two use. Used aluminum soda cans are abundant in many households, and they provide the best disposable aluminum container for autoelectrolysis. Cut these cans lengthwise using a metal cutter and you have two cylindrical cups for your work. Place the coins in them and cover with lemon juice.

Another method is to use a plastic tray in which you can place aluminum foils. Since aluminum foil is very thin it wears out soon during autoelectrolysis, and therefore you might have to fold them to create a layer of four sheets. Place the coins flat on them and cover with lemon juice.

Final Touches: The coins become totally free of all deposits through one or more sessions of autoelectrolysis followed by brushing. They should then be left in distilled water (battery grade will do) for a couple of hours to remove all traces of lemon juice. They should then be dried by placing them on absorbent paper. Dry them in sunlight for an hour or two.  You can polish them, if you wish, with soft cotton. Finally you can place then in coin holders or whatever you use to store coins.

Autoelectrolysis is a totally safe and gentle method for cleaning silver coins.  Begin your experiments with your cheapest silver coins in your collection, perfect the art, and then only clean your more expensive coins.