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Cleaning Ancient Coins
Cleaning away thousands
of years of dirt off of these ancient treasures requires a little
patience and some practice. Some coins will show detail through the
crud and will surface with some distilled water and a good brushing
with a stiff tooth brush. Some require more effort and time. Below I
will discuss my methodology for cleaning coins and point out the
advantages and pit falls of each type of method.
Water and Soap with a tooth
brush.
Items required: One 4" X 6"
plastic container, one Firm toothbrush, Distilled water & soap!
Considered Gentle Cleaning
Patina Change NONE
Place up to 50 uncleaned coins in the container
spread out across the bottom. Using distilled water and 2 drops of
dish soap cover the coins with at least 2 inches of water. Just
soaking for 24 hours in this solution will loosen and remove a lot
of the dirt. Now set up another container with the same solution.
Remove a coin from the first container and use the toothbrush to
scrub away any loose dirt rinsing with the water from the first
(dirty) container. After you have spent a few minutes scrubbing this
coin, rinse it and place it in the clean second container. Repeat
this process until all coins are in the second container. Now let
these soak another 24hrs and repeat the whole process. It is
important to change the water every 24 hrs because the natural
cleaning effect will be lost as the electro chemical properties of
the water are diminished by the lost free electrons that have
attached themselves to the dirt to free it. Many times this method
of cleaning is all you will need. Remember often times the patina or
color of the coin is the detail. That neat red, orange, green, or
black stuff is really the coin. So don't take too much off and
reveal the base metal as this will lessen the value of the coin.
Patina is the natural coloration of the coin after two thousand
years. A soft brass brush can be used in the beginning but use
caution as it can damage the coins surface. Using an aggressive
method on such a coin would only harm it. Remember that these thin,
handmade coins have weathered many centuries and are fragile.
Sometimes even a brushing will be enough to break them in half. It
is suggested that you should always attempt to clean a dirty coin
using the gentlest method available. It is sometimes the case that
dirty coins aren't so dirty after all and a simple brushing is
enough to reveal all the coin's detail.
Olive & Mineral Oil Soak
Items required: One 4" X 6" container,
one Firm toothbrush, Virgin olive oil or Mineral oil.
Acid base Cleaning
Patina Change Darkens
For stubborn coins with a lot of encrusted dirt that
refuse to come clean with soap and water this is the next step.
Soaking for a longer time in oil will penetrate and loosen the crud
on encased coins. A one week soak will produce good results on these
more difficult treasures. The down side is that the olive oil will
darken the patina because of the caustic or acidic base. Mineral oil
works as well and darkens the metal quite a bit less. I use mineral
oil. I have seen WD-40 used with fast results but it darkens the
patina worse than olive oil.
When your coin is clean you should attribute it as much as is
possible given the remaining detail. While it is not always possible
to fully attribute a coin because vital information is worn or
missing for some other reason, it is generally the case that you can
narrow it down to several likely rulers. Many, if not most, can be
at least traced to the emperor who issued it and thus a date range
for when the coin was minted is possible to attain. Many more will
be fully attributable as to not only emperor but also as to in which
city it was minted and sometimes down to the very year it was made.
Chemical & Acid baths
Items required: Vinegar, CLR, 4" X 6"
container, safety glasses, kitchen gloves
Acid base Cleaning
Patina Change Darkens Brass+Bronze Strips
Copper + Destroys Silver
The use of strong acids like muriatic, sulpheric, and yes vinegar
are in my mind an option that requires care and limited use. I only
use vinegar as a 5 minute bath on tough cases to break the surface
of the crud. Return the coin to the soap and water process after the
acid bath and test the crud with your toothbrush.
Ultrasonic Cleaning
Items required: One US Unit
Ultrasonic Cleaning
Patina Change NONE
Small home jewelry cleaners are not a choice! They
are too weak in the power department!
Larger more costly professional units do a nice job on most coins
but the process needs to be closely monitored so as not to strip the
coin and over do it!
Electrolysis
Items required: One 4.5VDC to
12VDC output wall transformer, Container with salt water.
Electronic Cleaning
Patina Change Removes all patina + Ruins
silver
Unit Construction Plans
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Click to enlarge Photos. |
Once you've attributed your coin as best as you
can you will want to preserve it for display or storage. If the coin
has not fared well in cleaning you may try restoring a suitably
"ancient" look by using one of several re-patina methods available.
If you are satisfied with the way the coin looks as is you could
give it any of a number of treatments (see "finishing") to keep it
looking its best. If you skip this step because the coin looks good
enough as it is you may find weeks later that the surface has
changed some because the metal had not yet stabilized to its new,
clean environment. Sometimes the coin will deteriorate and sometimes
it just looks a little duller. Either way, it's worth at least
considering a protective layer of some sort. I use a pinch of bees
wax finger rubbed into the coin. It seals the coin and protects it
from acids and oils from your hands. Some people use mineral oil or
3in1 oil but this needs to be lightly reapplied over time.
The final step is choosing a long-term storage
method. Many prefer to put their coins in 2x2 flips which can then
be written on with the attribution or other information. Others
prefer vinyl flips with inserts that carry the information. Doing it
this way allows easy retrieval and handling unlike the 2x2's but
increases the chances of the coin being misplaced. There are many
other ways of storing your coins of course, explore what suits you
best!
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