How to clean bronze coins
PLEASE READ CAREFULLY
ALL THE GUIDES POSTED ON THIS WEB PAGE ARE WHAT I HAVE FOUND TO WORK FOR CLEANING FINDS FROM MY OWN EXPERIENCE. I TAKE NO RESPONSIBILITY FOR YOUR ACTIONS, ANY PERSONAL INJURY, INJURY INFLICTED ON OTHER PERSONS OR DAMAGE CAUSED TO FINDS AS A RESULT OF USING THIS INFORMATION.
At the end of the day there is no definitive way of cleaning finds the way you do it is entirely your decision. What I am discussing here are a number of methods I use and what I have found to be successful.
The decision whether to clean a coin really depends on its age, rarity and its metal-alloy composition. The bottom line is DON'T clean coins except to gently wash them with water unless you can see any benefit of doing so. One example of a beneficial instance includes a situation where corrosion has obscured detail critical to a coin's identification and thus cleaning can be used as a method of information recovery. The following phrase applies not just too chemical cleaning but to all cleaning. “We must do it the right way and appropriately!” Polishing with abrasives such as Brasso, Silvo or any other metal polishing pastes or compounds is in my view the wrong way and possibly one of the most damaging things you can do. Using caustic chemicals such as ammonia or some other form of alkali whilst still not ideal is better than using abrasives and does not involve the kind of heavy handedness polish does. A WORD OF WARNING BEFORE USING CHEMICALS! YOU MUST WEAR SUITABLE PROTECTIVE SAFETY EQUIPMENT AT ALL TIMES INCLUDING SAFETY GLASSES, MASKS, CHEMICAL RESISTANT GLOVES AND APPROPRIATE CLOTHING WHICH ALL CONFORM TO CURRENT HEALTH AND SAFETY STANDARDS. ALWAYS OBTAIN AND READ THE RELEVANT MATERIALS SAFETY DATA SHEET AND READ THE LABEL ON THE BOTTLE OF THE CHEMICAL IN QUESTION BEFORE YOU USE IT. IF IN ANY DOUBT CONTACT THE MANUFACTURER OF THE CHEMICAL FOR PRECAUTIONS AND GUIDANCE ON PROTECTIVE CLOTHING, USE, STORAGE AND DISPOSAL BEFORE YOU PROCEED. MAKE SURE TO WORK IN A WELL VENTILATED AREA AND LABEL ANY CONTAINERS YOU USE WITH THE CORRECT HEALTH AND SAFETY INFORMATION. THIS APPLIES TO THE USE OF ALL CHEMICALS, MAKE SURE YOU WORK SAFELY AROUND YOURSELF AND OTHERS.
Gold no matter its age is a very stable metallic element which does not react with oxygen or minerals found in the soil. To our delight therefore most gold coins will be found in the much the same condition as they were when they were dropped. The only kind of deposites we are likey to see are those of the actual soil from where the coin was removed. Taking into account that gold is also quite soft and marks very easily it would be strongly advised to work carefully and slowly when undertaking soil removal restoration. The best approach here would be to use water and gently work with a cotton bud using a technique I call dab and roll cleaning. You simply dab and roll a wet cotton bud on the surfaces of the coin to loosen and remove the dirt. If some of the dirt doesn’t come off straight away then don’t be tempted to start rubbing and abrading, have patience and work consistently until you have achieved the desired results. If after exhaustive work the cotton bud technique fails then as an alternative use a very soft brush (small paint brushes are good for this) and slowly but carefully remove all remaining dirt from affected areas. Again don’t use the brush in great sweeping motions instead apply the same principles and try to dab with it. As I said before being gentle and taking your time is the key to success.
Silver is a little more reactive than gold but it is still reasonably inert when compared with other metals like copper. Silver does react with oxygen in the air and will also to a certain extent react with minerals in soil. Although silver is not inert like gold the process of corrosion is very slow therefore most silver coins will be found in good condition with perhaps a little patina. Before we talk about cleaning it is wise to note there is nothing wrong with a well toned coin and in fact many collectors like toned coins as evidence they have not been tampered with. If you absolutely must clean silver coins then the best way I have found to do it is as follows:
Use a plastic or glass open top container and gently pour an ammonia solution of maximum 25% concentration over the coin in question until fully immersed. Leave for around 5 to 10 minutes or until you are satisfied the undesirable corrosion has been removed. Sometimes using two cotton buds, one to hold the coin down and the other to work on the heavy corrosion can help speed up the process. Stirring the solution can also have a similar effect if you are unhappy using cotton buds. After you are satisfied with the results pour the used ammonia solution into a suitable, empty and appropriately labelled screw top container for reuse. Remember you don't want to be contaminating your freshly acquired ammonia or disposing of it if the chemical can be reused. It is worth noting at this point that you should never attempt to use metal containers, containers with bungs or metal screw cap lids for storage. Ammonia vaporises easily forcing bungs out of bottles and quickly eats metal containers and screw cap lids the result being corrosive vapours escaping into the environment. This you definitely don't want to happen! Now start to rinse the cleaning vessel and the coin under running water until all chemical traces have been removed. Once satisfied that the ammonia is no longer present it should be safe to extract the coin, dry it and inspect the results. If you want to take extra precautions and make sure all the ammonia has been completely removed then rinse the coin under cold running water for a further 5 to 10 minutes. Stabilizing can be achieved by following the instructions further down the page if required.
BRONZE AND COPPER COINS
Copper, bronze and brass are quite reactive and will readily oxidise when given the chance and hence coins from these alloys often don't survive very well when compared to their silver and gold cousins. Again unless serious corrosion has set in or you might see some benefit in cleaning such revealing hidden detail then leave well alone. If you do decide there is a reasonably good chance cleaning will help matters then I have found the following method works best:
Place your coins in a suitable open top container and start pouring a small quantity of ammonia solution (25%) over them. When the coins are fully immersed take the container to a well ventilated area and allow the chemical to dissolve the corrosion. As the cleaning commences it is a good idea to return once in a while and check on your progress. If you notice a build up of deposits on the container bottom stir the solution and insure homogenization. (Be careful when stirring don't splash! Use eye protection.) Depending on the amount of corrosion present you should start to see the solution turn a green/blue colour after a few minutes. Don’t worry the colour change it is quite normal and a good indication the process in working properly. When you feel enough corrosion has been removed save your cleaning solution for reuse, retrieve and wash your coins under cold water. After rinsing and being sure all traces of ammonia have been removed finally dry the coins with a cloth and inspect the results. As a quick tip when you have reached this stage sometimes lightly buffing the coins with wire wool can further enhance the appearance. Note, don't clean coins if they have a nice natural clean looking patina it is far better to leave these coins as they are. You will only destroy detail and end up being worse off than when you started. This applies particularly to Victorian bronze.
HERE FOLLOWS A LIST OF COINS AND HOW I WOULD APPROACH CLEANING THEM.
Iron age Gold Stater - Only use water to remove surface dirt.
Iron age Silver Stater - Only use water to remove surface dirt.
Iron age Bronze Unit - Only use water and soft brush, very rarely would I use chemicals. (Only clean with chemicals if heavily corroded and there is a chance of revealing hidden detail, otherwise leave well alone.)
Roman Gold - These are rare, only use water to remove surface dirt.
Roman Silver - Only use water to remove surface dirt.
Roman Bronze/Copper - Only use water and soft brush, very rarely would I use chemicals. (Only clean with chemicals if heavily corroded and there is a chance of revealing hidden detail, otherwise leave well alone.)
Anglo Saxon sceattas - These are rare, only use water to remove surface dirt.
Hammered Gold - These are rare, only use water to remove surface dirt.
Hammered Silver - Only use
water and soft brush, very rarely do I use chemicals. (Only clean with chemicals if heavily corroded and there is a chance of revealing hidden detail, otherwise leave well alone.)
Early Milled Gold before 1800 - Only use water to remove surface dirt.
Early Milled Silver before 1800 - Occasional chemical cleaning if very corroded otherwise I just wash with water and scrub gently with a soft brush.
Early Milled Bronze/Copper before 1800 - Occasional chemical cleaning if very corroded otherwise I just wash with water and scrub gently with a soft brush.
Late Milled Silver after 1800 - I do use chemical cleaning for late silver milled if I feel that it is worth doing and will enhance the coin.
Late Milled Bronze/Copper after 1800 - I do use chemical cleaning for late bronze/copper milled if I feel that it is worth doing and will enhance the coin.
Modern Clad Coins (Decimal) - I always use chemical cleaning and sometimes even polish, so that coins are clean enough to see what they are, just in case I decide to spend them!
REMEMBER IF IN ANY DOUBT TAKE YOUR COINS TO A PROFESSIONAL FOR ADVISE, BUT THE BOTTOM LINE IS DON'T CLEAN WITH CHEMICALS UNLESS YOU ABSOLUTELY HAVE TO. CLEANING CAN IN SOME CASES SERIOUSLY AFFECT A COINS VALUE IF DONE INCORRECTLY.
As a detectorist we will probably find more buttons than any other object and therefore a greater proportion of time will undoubtedly be spent cleaning them, so with that notion in mind it is probably a good idea to say a few words.
When using chemicals to clean buttons a cautionary approach is advised. Before making an ammonia solution you should try to asses the physical composition of the buttons you want to clean (Pewter doesn’t clean very well with chemicals.) as well as the level of corrosion present. Usually a concentration of 10% to 20% solution is enough to achieve the desired results without any negative impact. But a word of warning there are some situations where you have to be very careful, this is particularly so around any gilding and plating. Cleaning gilded objects is tricky at best and therefore chemicals should only be used as a last resort. A very weak solution of acid or alkali 5% concentration will be more than adequate for your needs. Remember you just want to clean the surface not completely strip it! Usually I only use soapy water and a soft bristled tooth brush but even then it's possible to do damage. In situations when I use chemicals I am always watching just to make sure I’m not removing too much.
Buckles are usually bronze, brass, copper, pewter or iron although you do come across the occasional one made from silver. This leaves us with a wide range of metals and alloys to be considered which is not to dissimilar to the situation we have with buttons. Choose your cleaning method carefully and be gentle, it is better to under do it than over do it. The same goes if you come across any gilding, try to go slowly and use the less intrusive methods first. Most of the time when I get buckles I like to leave them in their original condition and admire the green patina nature has provided over the years. If cleaning is unavoidable then start with cold water and a soft bristled tooth brush; if that isn’t enough then progress by adding a little soap. Failing that, make up a weak ammonia solution (5%) and see if that works etc. All the time check your results and keep records of your experiments, remember when it comes to cleaning knowledge is power.
Generally most people think of brooches as something of relatively modern invention but contrary to belief these items have been around since at least the Iron Age. As a result finds of this nature are often of great historical importance and interest to museums. Brooches were made in a wide range of shapes, sizes and materials therefore cleaning and restoration needs much forethought and consideration. Before starting work think about your options and be sure to weigh up the consequences. Always start with the milder cleaning methods first, a soft bristled tooth brush and clean water might be all you need. If the milder methods don’t work then progress to a weak solution of ammonia and try again. If you still have no luck then may be consider moving to abrasives etc. Remember you should always have an element of caution when cleaning and IF IN ANY DOUBT ASK A PROFESSIONAL FOR HELP! Contact your local museum they should be able to point you in the right direction.
Items such as musket balls and pistol shot are often the talking point of military historians and can sometimes offer great insight into the physical layout of an old battlefield. Being made from lead like most projectiles of the era they tend to be quite soft so cleaning them with a quick rinse under the tap is often more than adequate. WARNING! LEAD DEGRADES IN TO EXTREMELY TOXIC WHITE LEAD. DO NOT ATTEMPT TO ABRADE OR POLISH LEAD OBJECTS. AVOID DIRECT SKIN CONTACT, AVOID EXPOSURE TO WHITE LEAD DUST, ALWAYS STORE IN A SEALED CONTAINER.
When dealing with items which do not fit into the categories above use your common sense, if an object looks old then it might be valuable. Seek professional advice from a conservator before attempting any conservation work of your own. Remember if something is very old, say Bronze Age, Iron Age or Roman then it is usually much better to just to wash in water and leave it at that. Cleaning something incorrectly or without the proper advice could lead to irreversible damage and loss of information that can never be recovered.
If you are particularly worried about post corrosion and choose chemicals like I do for cleaning finds then it is a good idea to go through a restabilising process. This process removes even trace amounts of cleaning chemicals and other harmful compounds which may propagate post corrosion. Quite simply what you do is to take an artefact and place it in distilled water for up to three weeks making sure to change the water every day. What this will do is remove all harmful chemicals left on the surface of the metal by slowly leaching them out into the water. Provided the water is changed on a regular basis there will reach a point where all unwanted chemicals and compounds will have been removed leaving the object in a chemically more stable condition.
On drying some people like to beak their finds in an oven for a few hours to make sure that all moisture has been removed. However I find that this tends to darken my finds which to my mind is undesirable. So all I do is to simply let my finds dry at room temperature and wait until they are ready for storage. If you want to know more about finds conservation then contact the British Museum they will be able to give you lots more useful hints and tips. There is also some good information circulating around from the Portable Antiquities Scheme CLICK HERE which has more helpful advice on conservation. Again the overall message is the same; reserve cleaning for all the modern grotty stuff and leave the rest well alone.
Amongst the many cleaning methods available to detectorists I have found a barrelling machine to be one of the most effective. If left long enough the barrelling process will have no problem in completely striping away all that nasty dirt and corrosion. But hang on before you rush off and buy one! Therein is the inherent problem, it’s simply too efficient in most cases to be used on good finds. The process involves the use of mechanical wear to rub off surface layers of the objects being cleaned and therefore use on ancient, valuable and important finds is not recommended. Save it for the really grotty stuff; by this I mean badly corroded modern coins, buttons and maybe the odd buckle. I personally enjoy cleaning buttons in my barrelling machine and let’s face it detectorists get thousands of these every year! If you are interested in using a barrelling machine then I have found the following method works best:
First off you will need to find a retailer who will be able to give you what you need. Usually your local metal detector dealer will be able to help and even if they don’t stock directly they should at least point you in the right direction. When buying don’t go mad and get cement mixer! All you need is something that is able to handle a small amount of gravel, a pinch of tungsten carbide grit and some of your finds. If you are lucky, as I was, then most materials will be supplied as part of the equipment package, but if out of luck you will have to shop around.
Equipment and Materials RequiredSource: www.psdetecting.com