Cleaning coins
(or
how to reduce a million dollar collection to less than a hundred dollars with
just one spoonful of Brasso)
www.aussiecoins.com
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 cleaning rare coins with jex or acids and reducing a highly valuable
collection to worthless scrap metal in minutes. All 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 - and reject - artificial shine. 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 exactly as they are 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.
Copper coins
High grade copper coins do need a protective coating
to prevent fingerprints, avoidable toning and that green 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' paint brush - pig, ox or camel
hair. 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 clumsily handled by someone with
sweaty fingers. This may have happened 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. 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 always be
a black spot, often referred to as a carbon spot. There is no way to remove
this. Trying will always reduce the appeal of the coin. Some blemishes we just
have to live with.
Silver coins
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 on copper coins. Use a separate
brush and keep them apart.
Cupro-nickel coins
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.
Gold coins
Any visible grime can be removed with very gentle rubbing or brushing under flowing warm water. Soap or detergent will not hurt. As always, avoid any abrasion.
Storage
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.
You are welcome to contact us for further information.
aussiecoins@iprimus.com.au
December 2009