(or how to reduce a million dollar collection to less than a hundred dollars with just one spoonful of Brasso)
Coin cleaning is a complex topic, on
which experts have written extensively. Their general conclusion is - DON'T!
All coin dealers have encountered well-meaning amateurs who have cleaned rare coins with jex or acids and reduced a highly valuable collection to worthless scrap metal in minutes. All five King George V pennies from the period 1932 to 1936, for example, in uncirculated condition with natural dull lustre are worth between $400 and $1000. The same coins if artificially polished are worth between $20 and $50. Any dealer or serious collector will immediately detect artificial shine - and reject the coin. So if in any doubt at all, it is best to leave coins as they are. Especially if you wish to sell to a dealer or collector, leave them untouched for the best price.
But to ensure coins are kept in as close to original condition for as long as possible - hopefully forever - there are exceptions to this general rule.
High grade copper coins do need a protective coating to prevent fingerprints, avoidable toning and that greenish corrosion known as verdigris.
Our uncirculated copper coins are brushed with a light coating of pure natural olive oil using a soft animal bristle artists' brush. This light brushing with oil serves to remove any visible deposits of grime or verdigris. Just as vitally, it removes invisible contamination such as acid or salt deposits arising from being carelessly handled with sweaty fingers. This may have happened unintentionally just prior to acquisition. But it may only become apparent months or years later as a disfiguring black fingerprint.
We use a small paint brush of natural camel hair, though pig or ox bristle are fine. We then cut across the hairs with sharp scissors at a point about half the length of the bristles. This leaves a firmer, more 'bristly' brush end which more effectively removes particles lodged around the lettering and the rim. But being soft natural hair, the brush will not scratch the metal. After brushing the coin as required, we then dab it dry with a clean, soft, absorbent natural cotton cloth which we keep for this purpose only. A new baby's nappy is ideal. All oil must be removed except for the very lightest coating.
This very thin oil layer protects against further contamination without affecting the original lustre. Copper coins in lower grades, below very fine, usually do not need a protective coating. But this treatment may be useful sometimes to remove visible accumulations of grime or to arrest the development of verdigris.
Most copper specialists approve of this method of preservation - but this method only.
Note that after arresting verdigris or other corrosion, there will usually be a black stain, often referred to as a carbon spot. There is no way to remove this. Trying will almost always reduce the appeal of the coin. Some blemishes we just have to live with.
Silver coins are sometimes 'silver dipped' with the commercial product Tarn-Off or similar. This is regarded as acceptable by some numismatists, though not by all.
We prefer to leave silver coins as they are, with the original toning, even if it is a dull dark blue-grey or black. Our buyers may dip them if they wish. We believe that where an old silver coin has developed a silver-gold or silver-blue toning to the lustre, this will almost always add to the value of the coin rather than detract. Refer, for example, to the descriptions of the 1927 Canberra Commemorative florins on the silver coins page on this website.
Silver dipping fluids are clear acids of a watery consistency. These must not be confused with Silvo or Brasso which are thicker abrasive pastes and absolutely to be avoided. Silver dip removes the outer molecular layer of the metal, leaving an unnatural sheen. This gives the impression of being brilliant uncirculated. With later date coins, this is usually okay, as it is hard to tell the difference between a natural and silver dipped shine. Older silver coins, however, will always have an outer layer of oxidisation - variously referred to as lustre, sheen or toning - which when removed will be quite obvious to a dealer or serious collector. Hence many auction houses will describe a coin as 'silver dipped' in the catalogue to alert purists who prefer their early coins untouched.
To silver dip a badly tarnished silver coin, decant a small amount into a small container and gently drop the coin into this. You may then brush the coin carefully, as with copper coins, above. Then wash it thoroughly under flowing water to remove all of the acidic fluid. Dab dry with a soft absorbent cloth.
Never use silver dip with copper coins, as this will immediately create a highly artificial shine which will always reduce the coin's value dramatically. For the same reason, never use a silver dipping brush with copper coins. Use a separate brush and keep them apart.
Rarely do these need cleaning. But sometimes green verdigris can develop. These coins are 75% copper so the same chemistry applies as to copper coins, above. Hence natural oil may be used, but never acids such as silver dipping fluids or abrasives.
Any visible grime can be removed with gentle rinsing under flowing warm water, with light brushing if needed. Soap or detergent will not hurt. As always, avoid any abrasion.
Do not attempt to clean or touch in any way whatsoever.
After careful cleaning, coins should be stored in an appropriate holder such as the 2" x 2" white cardboard coin holders - stapled or self-sealed - or a Dansco supreme album. These options allow viewing of both sides of the coin but prevent contamination from solid particles, moisture or handling. Push-in albums such as the Dansco deluxe are quite okay for average circulated coins, but definitely not appropriate for uncirculated items.
Valuing your coins
Please refer to our paper on Valuing your collection (click here).
Sell your coins
If you wish to sell, there are several options.
Please refer to our paper on Selling your collection (click here).
You are welcome to contact us for further
Written December 2009, revised June 2010