For some coins it is going to be necessary to use tools that are more aggressive than the brushes. In these instances steel, brass and
diamond probes are good, especially for removing the upper layers of thick encrustation that can then be further cleaned with the
fibreglass, brass and steel brushes. You do need to be careful though as too much pressure can cause the probe to slip and potentially
put a scratch right across the face of the coin. Diamond points are the most dangerous for coins as they will easily scratch the metal,
but they are effective. Steel and brass probes offer a variation in hardness to suit different parts of the cleaning process.
It is possible to get probes with fixed and interchangeable tips that vary from fractions of a millimeter to a couple of millimeters in
thickness. The super fine points are used for getting into the smallest nooks and crannies of the legends and portraits. The thicker
points for grinding away stubborn spots of encrustation.
We mentioned it earlier, but we definitely recommend some kind of magnification when cleaning coins if you decide to use steelor
diamond tools. A stereo microscope (this is one with two eye pieces) of any make or model is an excellent choice as long as you can
get a magnification of at least as low as 10x. You don't need a high magnification for coins and we find 7x to 15x is optimal. Basic
microscopes are cheap these days and if you are going to clean a lot of coins they are a must have. You can also use magnifiers you
wear on your head, jewellers loupes that you hold with your eye, or standing magnifiers.
Not all coins should be cleaned but in many instances if a coin isn't cleaned you are never going to see any of the details. Some people
will argue cleaning a coin reduces its value, but as we a referring to only average quality coins from hoards the effect is actually going
to be negligible and can often actually increase the value. For example, if you have a coin that is so encrusted you cannot see anything
then it is worthless, but if when you clean it there is a nice bronze Ptolemy coin underneath then it is going to be worth a whole lot
more. You should never clean off the patina on a good quality coin, but with lower grade coins that have had a lot of wear without some
judicious cleaning you are never going to see the details. We recommend you read around the subject and decide what you are happy
We use two principal methods of cleaning - 'wet' and 'dry'. Here is the 'wet' process we follow to clean our coins when using distilled
water or olive oil. (Dry cleaning obviously uses little or no distilled water, with all cleaning being done with tools).
1.) When we first receive a batch of uncleaned coins we initially wash them gently in warm water with dish detergent (Fairy and the
like). This will remove all the dust and dried mud that has been most recently deposited on the coins. You will be surprised how much
dirt this removes on its own.
2.) Repeat the washing a couple of times gently rubbing the coins together in the palms of your hands while submerged in the water. As
long as you are gentle you won't damage the coins and rubbing them acts like an abrasive to remove more of the dirt.
3.) Finally get a stiff nail cleaning brush and grab a hand full of coins. With your palm open and face up in the water begin brushing the
coins with the nail brush until they have all fallen out of your hands. Do this a few times as it dislodges any loose grains. Don't waste
time cleaning one coin at a time at this point.
4.) The water will be really dirty by this point so pour it away and tip the coins in to a colander. Give them a good rinse to get all the
detergent off them.
5.) Tip them on a towel and give them a quick dry. If any coins are already clean (its unlikely but possible) pull them out. They do not
have to be 100% clean as you can finish them off manually one at a time. As long as the majority of the muck is gone you can pull them
out. If you want to make sure your coins are completely dry before putting them away you can heat them in the oven on a clean baking
tray. Put them in on a low heat for 20-30 minutes and this will drive off any remaining water. You can examine the coins every 5 or 10
minutes and you'll see be able to judge when all the water has gone.
6.) Put the rest of the coins in a large container with lid and cover them completely with Distilled (not tap or filtered) water. It is best to
have the water level at least 1cm above the level of the coins. Some people say distilled water does not work, but in our experience it
does. It will soften and attract small particles of encrustation.
7.) Every 24 hours give the tub a stir so the coins get a good mixing in the water.
8.) After 3 days drain of the distilled water (keep it) and repeat the washing and sorting in steps 1 to 5. Any coins that still need washing
should be put back in the container and the distilled water added back in. Unless the distilled water is completely filthy you do not need
to replace it.
9.) Repeat all the stages mentioned in step 8 for about two weeks. This is a slow and steady method that is surprisingly effective.
10.) After the final cleaning and sorting at the end of two weeks any coins that are not cleaned to your satisfaction (which will be a good
number of them) should be put back in the container and this time covered with olive oil. You can keep or discard the distilled water at
this point. Again the olive oil should be at least 1cm above the top of the coins.
11.) Every 24 hours stir the olive oil and the coins so they get moved around and turned over if possible. This lets the oil get onto any
surfaces of the coins that might have been previously hidden. At this point it is important to note that you want the cheapest olive oil you
can find. Not Extra Virgin, you want the stuff that contains a percentage of refined olive oil as it is more acidic and attacks the
encrustation more rapidly. It does not damage the coins or the patina. In cooking you want the best olive oil, for cleaning coins you want
cheap and nasty! Some people say olive oil has little or no effect on coins. We disagree as in our experience it works really well. You
have to be patient, but try it yourself and we think you'll like the results.
12.) At the end of 14 days it is time to wash the coins. Drain off the olive oil and put it to one side even if it is green (and it will turn
green as it absorbs the dirt) as it will still be usable. Place the coins into the colander, add a generous amount of dish detergent, add a
little hot water and rub all the coins together in your hands. This will help remove the excess olive oil. Wear rubber gloves to stop your
skin drying out. Rinse in hot water and repeat as necessary until the olive oil is gone. As you do it you will see dirt really coming off the
coins. Once the excess oil is gone you can repeat steps 1 to 5. We spend about 20 minutes washing and gently rubbing/scrubbing the
coins. The water will probably be filthy when you have finished, which is a good sign.
13.) When you have pulled out any coins that are cleaned to your satisfaction return the dirty ones back to the olive oil for another two
weeks and stir daily as before.
14.) At the end of the first month clean the coins again but this time replace the olive oil if it is dark green. You can stretch it out longer
but we like to be able to monitor the progress by how the olive oil changes.
15.) At this point we just keep repeating steps 12 to 14 until all the coins are clean (it can take a year, so be patient). You will reach a
point where at the end of a two week period you'll have been able to pick out very few cleaned coins and there will be some that look
practically the same as they did when they first went in the oil. At this point you may want to try more radical chemical cleaning which
we will cover later.
The images below show two different batches of coins. The first was taken as soon as the coins were put into a litre of olive oil, the
second shows another batch that has been in olive oil for a month. The difference is obvious and all the discolouration seen in the
second image is due to breakdown of the encrustation and the particles moving into the olive oil. The final image is another comparison
between the two and shows there is some definite cleaning taking place.
Chemical preparation is usually a last resort, but some coins can sit for years in olive oil with no visible details ever being revealed.
Without the use of chemicals they would never be worth keeping. Although the original patina of the coin will be lost, actually being able
to see the details of the coin rather than throwing it away as trash more than compensates. We do not recommend aggressive
cleaning of coins unless as a last resort. If you have a particularly good coin it is best to just leave it alone. We recommend doing
several experiments with your worst coins if you want to use any of the following. You can then judge for yourself how to proceed.
Method 1 - Lemon juice.
Some people add lemon juice to their olive oil as the increased acidity increases the rate of reaction. However there are drawbacks and
1.) Only add a small amount of lemon juice to the olive oil to start with so you can see how it reacts. You need to stir it really well so the
the lemon juice is suspended as micro bubbles in the oil. The olive oil will go cloudy. Add the coins.
2.) While experimenting we would recommend checking on the coins every 10 minutes for an hour, then every 20 minutes for the next
hour and every 30 minutes for the next hour. This lets you gauge how the reaction is going.
3.) Every time you check the coins you will need to stir the mixture. This is because the lemon juice will begin to separate from the olive
oil. Also, as the mixture is never really mixed you are essentially letting fine droplets of lemon juice sit directly on the coin surface, so
you want to move them round to get an even clean.
4.) You can leave the coins in for longer periods but you do need to check on them and keep the mixture stirred. You can leave it
overnight if desired. Just be aware leaving the mixture for too long unattended with result on complete separation of the lemon juice and
olive oil - you'll be left with pockets of lemon juice within the oil meaning many coins are simply just sitting in oil with no added benefit
from the lemon juice. Alternatively you may well end up with a drop of lemon juice just on part of a coin, which will result in this part
getting a good clean while the rest does not, leaving the coin with a blotchy appearance.
We don't use this method often as it can be hit and miss due to the way the lemon juice separates from the olive oil.
Method 2 - Liquid Descaler
Another method some people use is exactly the same as that mentioned above except you use liquid descaler (the stuff you use to
remove lime scale from your kettle and can be easily obtained from any pound store) instead of lemon juice. You mix the descaler and
olive oil at a 50:50 ratio. As before you've got to mix it well and attend to it regularly as the descaler and olive oil will separate into two
distinct layers - the descaler settles to the bottom of the jar with the olive oil sitting on top and the coins end up just sitting in the
descaler. What we do is simply remove the olive oil completely from the equation and place the coins directly in the descaler. We
closely monitor them as the descaler will strip the coins back to the base metal. They will look almost brand new when they first come
out but do slowly darken over time. We only use this on the most stubborn of coins.
When you take the coins out of the descaler (every 10 minutes until you know how the coins are going to react) you will want to wear
some rubber gloves. Hold the coins in your hand and run them under some hot water while scrubbing them gently with a nail brush.
What you will see is black encrustation just slough off the coin. You don't want to get this on your fingers as it is horrible stuff to
remove. Gradually the encrustation will get thinner and thinner until metal starts to show through. You can stop at this point and return
the coins to a traditional olive oil bath or you can do manual cleaning. If you want to go back to the base metal leave them overnight in
the descaler then wash them in the morning. You might need to repeat this process but most times one night in the descaler will strip off
all the encrustation and patina and you'll be left with a shiny copper coin. Do not do this with good coins!
The images below show a coin before and after descaler treatment. You can see how the coin has been taken right back to the metal.
This will darken up over time to quite a pleasing hue but it is an aggressive form of cleaning and should be reserved for only the most
IMPORTANT: You cannot leave the coins in the descaler for days on end as it will have an adverse effect on the coins. They will turn
green, the metal may take on a bleached appearance and new chemical encrustation can appear. After an overnight cleaning in
descaler we recommend rinsing the coins thoroughly in hot water, drying them in the oven or with a hear drier and then placing them in
distilled water overnight. Doing this should remove all traces of chemicals from the coins. At this point you can do another overnight
descaler bath if required - just be sure to monitor the coins to make sure they are not being degraded.
Two other coins, this time Byzantine folles, that were gently prepared with a brass brush are featured below. Each one of these was
cleaned for just 20 seconds. You can see how the coins have cleaned up nicely and that there is very little polishing to the coins. Again
most light areas are due to camera flash. The brass brush is the one we personally use the most.
There are various types of pen brushes you can use to clean coins - Steel, brass and fibre glass. Each contains a fine wire/filament
bundle that removes dirt and encrustation from coins. They are typically used after washing and olive oil treatment. As with any coin
cleaning you use only a light touch. The goal isn't to bore a hole in the coin but to just gently abrade away the encrustation. We
recommend cleaning all coins under magnification, then you can really see where the encrustation ends and the coin begins. With care
you can quickly and efficiently remove much of the material obscuring the coin. You can use up and down, side to side or circular
movements, whatever you deem necessary to clean the coin to your personal standard.
The steel pen is the most abrasive brush available, and it is not for the inexperienced as it can damage the surface of the coin if you
are not careful. Steel is used on tougher or thicker encrustation before moving on to the brass and then fibre glass brush.
Brass is a softer metal than steel and in most cases softer than many of the bronze or copper coins you will encounter. Used in exactly
the same was as the steel brush it works well on all but the thickest encrustation. The images below show average quality Islamic
copper coins after olive oil cleaning that we cleaned in about 20 seconds with a brass brush. The first three show the progression of
the cleaning, the final image shows the contrast between a cleaned and uncleaned coin surface. The brass brush will give the coin
surface a light polish, but this can be kept to a minimum or avoided all together by using a light touch. If a little more time was spent on
the coins they would look even better. Most of the light areas showing on the coin are due to reflection of light from the microscope light
source and not excessive polishing.
Fibreglass brushes are used when a gentler clean than either steel or brass is required. It is designed to remove the lightest
encrustation and will cause no damage at all to the coin surface. One point of note is that as the filaments in the fibreglass brushes are
usually densely bundled their cleaning is largely confined to the high relief parts of the coin. What this does is highlight the legends and
busts while leaving the interspaces with some encrustation. This gives a nice contrast between the cleaned and uncleaned areas but it
can sometimes look a little too polished if you go too far. As with all cleaning, though, practice and experience will let you know the right
tool for any task and how much cleaning a coin actually needs (if any).
This is important, when using fibreglass brushes (in fact really when you do any dry cleaning) we highly recommend you wear a
face mask so that you do not inhale the dust. Fibre glass wears down gradually as you use it as an abrasive and will release tiny glass
particles into the air. These should not be inhaled. When we clean coins we have a small desk fan blowing gently across our work
surface and wear a face mask (offered below). It is much better to be safe than sorry. Also, when you have cleaned part of the coin you
will find an inclination to rub the coin with your finger so you can see where you have been. Do not do this as small glass fragments
can embed themselves in your fingers. Use a small brush, cloth or wear surgical gloves.
The images below show another coin from the same batch as that illustrated above. This time all the cleaning was done using the
fibreglass brush alone. You can see how the high points really stand out. The second image shows the coin after a few seconds of
cleaning. The high relief is already quite prominent. The final image shows the coin having been deliberately cleaned until the polished
finish is evident and even some interspaces are clean. The final finish you desire is purely a matter of choice, but we would recommend
keeping the polished look to a minimum, especially on better quality and higher value coins (which shouldn't really be cleaned anyway).
Now take out all your cleaned coins and examine each one closely. There may be patches of encrustation that haven't quite come off.
This is when you can begin manually cleaning the coins using some of the tools on our accessories page or return them to the olive oil.
Take your time and be gentle. Use magnification if necessary and you will be amazed how much the coins can be improved. With trial
and error comes experience and you will soon know exactly what you need to do to get the coins looking exactly how you want them to.
Start with the poorest quality coins first and go on from there.
We should mention that some people bypass the washing and soaking steps completely - as soon as they get a dirty coin they go
straight to manual cleaning, removing all the dirt with tools like those offered below plus fine brushes and tooth picks. This is a perfectly
acceptable way to do it, we just find using water initially gives a big head start by removing a large quantity of the most recent dirt. It
also saves time in the long run as cleaning every coin manually will take countless hours whereas with soaking you can leave the coins
unattended and simply let the liquids do their job - all you have to do is spend an hour every two weeks washing, scrubbing, drying and
sorting (we find you can get 2 kilos of coins processed effectively in an hour).
|The coins show above were left in descaler for an extended period of time. You can see the
adverse effect it has had on the coins by staining and bleaching the metal.