Metal Detecting: How to Clean Coins
I have decided to share with you the readers, some sections of my eBook 'Metal Detecting: How to Clean Coins'
Firstly, cleaning coins that you have found is not however, always the best thing to do when you have found a new coin or hoard as it can significantly devalue the coins and in a lot of cases deface the coin itself. There are many different methods to clean different types of coinage and this is where this eBook is going to come in handy and make sure that you never use the wrong method again. So if you are new to metal detecting or a seasoned detector looking for some new cleaning techniques, hopefully this eBook can provide just that.
It is always important to know your coins beforehand and get an in-depth knowledge of the coins that you may well find in the areas that you metal detect in. This knowledge combined with the techniques I am about to share with you will make sure that you are correct in which methods you use on your new finds if you do decide to clean them, resulting in the best outcome possible to put them in a show case, sell them off or put them back in circulation.
Just remember that not all clean coins are valuable and dirty coins aren’t always junk!
Coins and Corrosion
The first thing with coins is the importance to know the meaning of the two terms that are corrosion and oxidation that occur in mostly all found coins out in the field unless the coins are newly dropped. Corrosion is naturally occurring during chemical changes in the metal surface of coins or within the entirety of the coin. Oxidation of the coin includes all processes in which substances absorb oxygen or give off hydrogen. Coins are made up of many different types of metal that include gold, silver, pewter and many more. Here I will share with you the details of all metal types used within currency.
Coins in the Field
When out in the field we come across many forms of coins and many differences in their appearance when and after they come out of the ground. After time we will come across singular coins, multiple coins, coin dumps and ever if we are lucky hoards and caches of coins! Knowing what to do when it comes to these very different finds is extremely important as we want to remove the coins as easily and gently as possible without doing damage to the coins, land or ourselves!
Singular coins for example are the easiest coins that we will come along that are easy to remove unless coated in cement and will often be easy to free from loose dirt. Other times these singular coin finds may be coated in thick mud or dirt and will be best handled later on when at home under better conditions and in doors where we have more tools at hand and easier access to running water. Other times we may come across hoards of coins and caches if we are lucky where the coins are seized together in big clumps of mud, dirt and clay. These are going to be harder to remove and may cause damage to ourselves by trying to haul out a big chunk of mud pebble dashed with coins or come to be fed up of being hunched over getting fed up trying to force away coins one at a time. To get around this I would recommend keeping some tools in your pack or vehicle just in case you come across this kind of find. After all you should be planning on coming across any possibilities! My first steps would be to try to separate the Coins. Attempting to separate the find into more sizeable chunks. I would then go about trying to free individual coins from the dirt by using a brush and toothpick. If the soil however is hard then I would go about striking the dirt with a rubber mallet lightly and steadily until the coins start to budge. If this technique was to however damage any of the finds then I would take the find back to your vehicle chunk by chunk and once back to your home use a rinsing method of warm water. If they are still refusing to budge then set up some water with a baking soda mix added to it. If however the coins are not copper brass or bronze and they are likely all to be of silver or silver allow consider using a sulfuric acid solution instead.
This method could also be applied by boiling the coins and dirt in the solution for a short period of time to let loose the materials that are encasing the found materials.
Metal Types Used in Coins
Gold and gold alloys
Gold does not oxidize apart from a tiny part that is invisible to the naked eye that is a thin film. It also is not attacked by any acids and only has some very minor discoloration occurring. Pure gold is never used within coin making though as gold could never be prepared in pure state and has excessive softness which is no good for coinage. The use of pure gold in currency is no longer viable due to the price of gold! Some basic gold alloys are white gold which is consisted of 90 percent gold and 10 percent silver, Electrum which is about 35 percent gold and 65 percent silver.
Silver and silver alloys
Silver is the most frequently used metal in coinage due to the ability of how easy it is to be found and the wide ranges of locations it is found at. It can also be easily obtained from ore and is not too soft to use as coinage. It also is the right density to work with as it isn’t too hard to work with. It is an easy coin to build that represents the rough value of the coins there were to be made. Silver coinage always consist of silver alloys as chemical reaction occurs in non-silver alloy. Silver is often alloyed with copper as nickel is not a plausible alloy to silver.
Copper is the most used metal when it comes to non-precious metals. It can be attacked by weak acid and sulfur compounds. Although after time the copper patina forms a second coating which can be a mark of genuineness of age (not faked age) which should not be removed! Copper was regularly used in its pure state for coinage in ancient times but rarely used when it came to the middle Ages. The Middle Ages was where it was often employed as an admixture alongside silver to create white silver.
Platinum was a metal used in Russia between the years of 1828 up until 1845 and in other surrounding countries such as Poland, Venezuela, France and Spain. This was used as coinage as platinum has very high resistance to the effects of air and soil making it a good choice in coin making. It does not oxidize apart from an extremely thin film that is invisible to the naked eye. It is used as a bullion metal!
Nickel is the hardest metal that is used within coinage. It is a good metal as it does not oxidize or tarnish by sulfur compounds apart from like platinum where is creates an extremely thin film that is invisible to the naked eye. It is mainly used within alloys where the alloy is then changed from a red metal to a white one.
Zinc is very prone to surface oxidation which leads to its original pale silver look to become even paler as the coin gets older. This material has only been used in coinage in times of hardship and as almost an emergency alloy! However zinc is highly protective of its co-alloy and has never needed a protective additive!
Iron is also extremely prone to oxidation which then leads to rust. Like zinc this is another downfall to this metal within coinage and leads it to also be only used in times of hardship within coin making! Unlike zinc iron is extremely prone to rust so it has a zinc film.
Lead has been used surprisingly for coins on different occasions but due to its softness of quality and its quick loss of quality in air alongside recent studies of lead poisoning this isn’t a metal that is used with coinage and if found should be handled with gloves and washed/cleaning appropriately due to its decline in structure within water.
Tin is easily melted at a low heat and is not prone to oxidation at all hence it’s use in food storage! But its main downfall is its lack of strength. It is still used however in copper alloys!
Aluminum is prone to oxidation when it has a wide dominant surface and Because of this and it’s none hardy form it is generally used as an alloy and amongst cheap coinage. However it has been used in some Scandinavian and German coinage in the past!
As copper was one of the most used alloys I will now go into the details of some of the most used mixtures!
Gun Metal is an alloy of around 88 percent copper to a rough mixture of 10 percent tin and 2 percent zinc which is used for making cannons. Nickel consists of a mix of 75 percent copper and 25 percent nickel. There is a specific mix called Franklinium which is a cupro nickel alloy which was developed in the USA by the Franklin Mint. Bronze coinage consists of a mixture that is of 90 percent copper to 10 percent zinc ratio. Brass which was highly used in roman times was consisting of a copper mixture with 10-50 percent zinc. Pewter which was originally an alloy of tin was 15 percent lead and sometimes antimony and copper. These days modern pewter is usually lead free and contains copper and a small amount of tin due to recent discoveries of lead poisoning! German silver, Virenium is an alloy of 30 to 60 percent copper to a mix of 20 to 40 percent zinc and 10 to25 percent nickel. Potin which occurred in ancient times was an alloy of copper, tin, lead and silver mixture. Then we have Aluminum Bronze. A gold like and extremely hard alloy which consisted of 90 95 percent copper and 5 to 10 percent aluminum.
Some natural changes that occur in copper and its alloy mixes are extremely complex when it comes to the reactions and involve many chemical compounds and formulas so I will note a few here!
Copper Tarnish, copper oxide, copper carbonate and bronze disease!
Some copper patinas are as followed.
Green patina is that of a leafy green to almost bluish green patina. This can occur in the form of basic copper sulfate which can occur from the sulfur dioxide content of urban air. There is also a dark Green patina in green copper which is formed from the transformation of copper oxide by Acetic Acid which is present amongst our atmosphere due to emission gases. This then brings us over to red patina. Which can differ from bright red to a dark red or violet. This reaction consists of Cuprous Oxide or Copper oxide which is produced by the decomposition of organic matter of the soil. Finally there is brown patina which is a very thin film of reddish black Copper oxides founded through the reaction of oxygen. This can also be a mixture of red or green!
I myself and other metal detectors, coin collectors and archeologists will not remove the patina as this shows a true sign of age and once the patina has been removed it can give way to bronze disease! Patina on coins is so relevant in the proof of age that expert fraudsters will go out of their way to forge coins and develop techniques to fake patina on coins!
When you find coins in the field do not and I repeat do not! Rub dirt off them with your fingers as this can seriously damage the face of the coins. If you are keen to have a quick look to what coin or coins that they may be then use a fine toothbrush to gently knock any dirt or mud off until you get an idea of what the coin is. I prefer to use this method then to place the coin/s in a coin pouch or tin filled with cotton wool then I can carefully clean them once I arrive home! It is actually known that just wiping the dirt from a found coin can drop its grade and its value rapidly if the coinage is rare, sometimes the rarity can drop so severe that the price of your find could drop in value as much as few hundred pounds if it is of such rarity! As noted above it is always better to read dates and mint marks of any suspected silver coins once you arrive home. You can remove dirt carefully out in the field though just wear gloves!
The best way to go about coin shooting is to do your research on the coins that you are most likely to come across in your area! Research is always the key and this can lead to quick analysis of your finds and possible rarities and enable you to act quickly and get on with finding your next item without rushing to brush off, clean or store any finds! Another good idea is to have a handy pocket sized coin guide for your coins in your country! Don’t always think that a shiny coin is an expensive coin and a dirty coin is worth nothing, this is very much not the case!
Before cleaning any coins it is key to figure out the type age and rarity of the coin, then once you have determined this you can go about using the best method in cleaning the coin if it does need cleaning. I would clean most coins by using a toothpick to lightly pick out any moveable dirt from any indentations after using a soft toothbrush to lightly knock off any dirt. After removing any dirt (not cleaning the coin) you can start to think about whether or not you want to actually clean the coin. If it is rare and valuable it is best not to do so, this also is the case if you want to sell on the coin to any buyers! You may think that buyers want to purchase cleaned coins but this is often not the case as you may damage the coin and value and this way you are leaving the buyer to make that main decision. If you are however going to be placing the coin in your own collection or the coin is quite standard you may want to clean the coin so it looks presentable and you can see all the details there are some many different ways to go about cleaning them!
Distilled Water Freezing
This method has been used by archaeologists where they will place the coins to soak in distilled water then placing it in the freezer, the coins will sit tight whilst the water penetrates all of the crevices and dirt whilst the ice crystals expand and break it away from the coin. This method takes a good few goes but is proven to be quite effective after a couple of goes!
Another method that is highly effective. By getting a shallow bowl of ammonia (enough to cover half of a coin) you can dip the coins in and polish off the coins to a nice finish. This method works best with gold and silver coinage! See immersion baths for this technique
Coin tumblers are amazing for speed and cleaning coins by the many but these devices are not to be used for coins with any historic value as you are highly likely to damage and scratch the coins. It would be like putting brand new wrist watches in a washing machine and expecting to not have scratches upon the glass afterwards. These are only good for your finds that you aren’t too fussed about, are going into a collection of odds and sods or going into your kid’s piggy bank or back into circulation!
This is one of the simplest techniques of Elctrochemical reduction cleaning. This technique however should not be used on silver coins that are of a high value. To use this method, take a silver coin and place it into a strip of folded up aluminum foil making sure that the shiny side is facing inwards. The foil and silver coin should be slightly moistened separately with a tiny bit of water before placing the silver coin inside the aluminum foil sheet. Once the silver coin is placed inside the foil and the coin is surrounded by the foil at all sides quickly press and indent the foil into the coin's grooves using your fingers and thumb making sure to not keep your fingers upon the aluminum foil for too long of a period as the chemical reaction between the foil, water and the oxidized silver may start to create heightened temperatures which could leave to burns on your skin. This chemical reaction should last for several minutes. After the coin has cooled down again gently peel the aluminum foil away from the coin. You should notice Blackish oxide on the coin that can then be easily rinsed off of the coin and wiped down with a soft cloth or towel.
Cleaning Gold Alloy coins
Luckily for us gold does not oxidize to full extent other than an extremely thin layer that isn’t visible to the naked eye. It also doesn’t combine with sulfur and is not effected by hardly any acids! Sadly to us who go out metal detecting and for coins and gold who wouldn’t mind a good turn over on some of our finds of gold coins I’m afraid to say that pure gold is never used within coinage. Some minor discoloration sometimes occurs within gold. I have found that the following few methods are the best ways to go about the cleaning of gold alloy coins. Because of the density of gold is very soft and prone to dings, scratches and scuffs I prefer to clean gold coins by hand other than the use of any of the above methods in which contain abrasives! Wet Cleaning with the coin being submerged in warm soapy water for an hour or two. Turning the coins over every fifteen to twenty minutes whilst rubbing the coins with your fingers or a wet microfiber cloth. A water solution fine salt or a very fine reduced ammonia solution can be used also. The other method of cleaning that I would recommend with gold alloy coins would be to simply buff them with a jeweler’s cloth using the above method beforehand to get rid of any serious dirt from the coin! As most gold coins will have considerable value especially with today’s markets I would highly recommend that any seriously dirty or damaged coins once identified should be taken not cleaned to a coin expert to have it valued as the dirt will not lower the price!
Cleaning Iron Coins
Iron coins are most subject to rust which can easily be removed by some very simple home methods that are used around the world by many people including the method of coca cola which is used to demonstrate to children how bad the drink is to their teeth and insides! To do this you can simply add a coin into coca cola and let it sit over night or take it out after an hour or two! Other ways of removing rust from iron coins are by soaking the coins in dw40 or petroleum and buffing with a rough and then soft cloth! After cleaning any iron coins in the ways I have explained here or any other methods that you find online or in other books you must be certain to dry your coins properly to stop any discoloration.
Cleaning Copper and Bronze Coins
Copper and bronze coins can be cleaned by several of the methods above by using soaking methods and brushing methods. Another method that you could use is by using a salt or baking soda solution and bringing the water to a boil in a bowl that is submerged but still sturdy within a cooking pot. You can also by general cleaners for copper such as copper soap and also consider the hydrogen peroxide immersion technique.
Cleaning Aluminum Coins
Aluminum coins are scarce in collections other than being in that of mint state due to the rarity of circulation. These coins take to oxidation extremely easily and are passed off as unwanted by collectors if they show any traces. Chemical treatment is a no go when it comes to cleaning aluminum as this is one of the metals used within coinage that is attacked by Sodium Hydroxide. The only methods I know of that can be used for cleaning aluminum really is the use of a Hydrogen Peroxide immersion bath which is performed extremely quickly. The only other way of cleaning aluminum that I know of is to get rid of any aluminum Tarnish by washing the coins in hot soapy water. Again this has to be performed extremely quickly and followed on by a good drying of the coins by patting them dry.
Cleaning Zinc and Tin Coins
Zinc and tin was used only for coinage in emergencies and times of hardship and so these coins are hard to find and not very often come across! Zinc coins however can be done more vigorously by mechanical hand cleaning with a hard brush or mixed with a hard brush in soapy water! Tin coins on the other hand are best cleaned by using a diluted Hydrochloric acid solution. Being taken out and rinsed often and buffed to a shine by using a light cloth and chalk powder.
Cleaning Lead Coins
Lead coins aren’t a highly found item due lead not being a well-used metal within coinage but if you are lucky enough to come across lead coins then the best way to clean them is by using a Caustic Soda solution by placing the lead coin in a mixture of sodium hydroxide and methyl alcohol! After you have thoroughly washed the coins they are then removed and heated up in a solution of lead acetate which contains acetic free acid. This can be repeated until you have the desired cleanliness of your coin/s!
Purchase My eBook Below
If you want to learn more on coin cleaning techniques such as submersion baths, electrolysis and coin polishing then click the link below for your copy of my eBook
Metal Detecting: How to Clean Coins