Cleaning and Treatment of Ancient Metal Artifacts and Coins
Part - 2 - Two
The cleaning of antiquities, and coins in particular is a subject of much debate in the collecting and scientific community. Some believe that ancients should never be cleaned or altered, but should be left entirely for future generations with better technologies of restoration, while others don't hesitate to throw whole piles of ancient coinage in the harshest acid baths and rock tumblers. A wise course, it seems, is to pursue a middle ground, evaluating each coin or object on its own merits and needs, and using cleaning technologies appropriate to the specific conditions found on the surface of the artifact.
Further, one should note that, because the deterioration of a coin's surface over time is rarely uniform, the best cleaning techniques will apply different techniques and skills to different parts of the coin or artifacts surface as appropriate.
I recommend doing your cleaning experiments on cheap coins and artifacts. You will destroy some pieces in learning. Hopefully the percentage of items that you damage will decrease as you gain experience. Always do a little experimenting with lesser pieces before trying to clean an important piece.
Keep in mind that the layers of patina on your coin or artifact are, unless they are of a destructive type, the best protection that your item has from the environment. The stable boundary provided by a good patina provides a chemical and mechanical buffer that can protect a coin or artifact for thousands of years. Once an item is cleaned, the rate of deterioration increase several hundred times over until a new patina or tarnish layer is formed.
Whatever the method you choose in cleaning an artifact, the ideal objective is to uncover a protective, attractive patinated surface if such exists. In some cases the encrustation will have no such layer underlying it, and the objective will be to thin the existing encrustation to show more detail, or to remove it altogether. The only reason for cleaning an item, and thus a prime consideration in the process, is maximizing attractiveness.
There will not necessarily be any easy way to clean a given artifact, but here are a few guidelines for general approach:
1. Choose simple washing and olive oil first, over mechanical means, and choose mechanical means over chemical techniques.
2. For best professional results, Choose localised techniques over global ones (alter the areas of the artifact that need alteration, and not the whole coin)
3. It is better to stop to soon than to late.
Always restabilse any object exposed to chemicals in the cleaning process.
Again, let me repeat for clarity's sake. If you try cleaning ancients you will ruin some of them. The information following should give you a good start. I will list the techniques from safest to least safe for the artifact - You are responsible for your own knowledge in handling chemicals, which you choose to use, in a safe manner. Good Luck!
Water: Repeated soaking and washing in plain or distilled water is generally safe and appropriate for the removal of simple dirt and clay accumulations. A toothbrush may be used for greater effectiveness.
Soap and Water: Household soap, detergents, and shampoos are effective in cleaning many items that are lightly encrusted. Effectiveness is increased by the use of a toothbrush or other stiff bristled no metal brush. Soap and water is minimally effective on patina type encrustations
Olive Oil: Soaking bronzes in Olive Oil is the oldest and most reliable and least destructive cleaning technique that I know of. You cannot leave an object in olive oil too long. This technique has been used for hundreds of years, and it is the only cleaning technique of which I have never heard a condemnation.
It is, however, also the slowest technique I know of. You may not see any results for a month or more, and complete cleaning of an article can take many months. Some encrustations will not respond at all to this technique. It is, however, the only technique other than microscopic cleaning with hand tools, that I personally will use on expensive or fine coins.
To speed up the cleaning process the temperature can be raised, but you need a thermostatically controlled cabinet to regulate it. The oil should not be heated to above handleable temperature. Don't use gas burners or ordinary electric hotplates to heat the oil! Olive oil is very flammable.
Too use olive oil, place the object to be cleaned in olive oil in a closed container. To hasten the process, use a toothbrush to occasionally gently scrub the coin. Change the oil monthly or bi-monthly.
High Pressure Water and Mechanical Washing:
Techniques such as water picks, dishwashers, and placing items in a sock in the washing machine are potentially effective in removing dirt type encrustations only. Beyond this you will need to use your judgement as to the potential effects on fragile artifacts and expensive appliances.
Ultrasonic: Ultrasonic cleaning devices are useful for removing loose layers of dirt, and they are to some extent effective on more permanent encrustations. With a good ultrasonic device, the crud will just fall off, but over cleaning is possible. This process is very gentle, but many ancient items are structurally fragile or brittle. The can shatter, break, chip, or develop shiny spots if left in too long or if they were weak to start with. Note, the cheap ultrasonic jewelry cleaners you can get on eBay are sufficient for this purpose. Mine cost $90.00 last year on eBay.com.au .
Brass Brush: The brass brush is a fast and usually safe approach for preliminary removal of dirt and clay deposits on bronze items. Some people hate this technique, some love it. I have tried it with great results in some cases, and damage to the artifact in others. The real trick lies in knowing when to stop. Some brushes are too hard and will scratch your coins, some are to soft and will rub off a layer of brass on your items. I like the brass tire and suede brushes manufactured by Kiwi (as in the shoe polish). You can find them at Coles or Woolworths/Safewaty. Never use this technique on a high quality coin, or on any item made of gold or silver.
Tumbling: Using a rotary rock tumbler to clean coins is generally a bad idea.
Vibrating tumblers of sort used in jewelry trade are somewhat better. There are many different kinds of media for use with this type of tumbler, from walnut husks, to wire clippings, to steel shot, and fast cutting ceramic and plastic abrasives. The results, therefore, can vary from the equivalent of a gentle scrubbing with a toothbrush in soapy water, to the equivalent of sand blasting away half of the mass of the article. A remarkable degree of control is possible with a lot of information and experience, and efficient destruction is possible without. The challenge here is that a tumbler of this type is a fairly high tech piece of equipment that must be used correctly with the correct media, time, soap, and judgement about the condition of the article. Experience and knowledge is the key.
Dremels and related tools: While they are wonderful tools, there is absolutely nothing that I have discovered to date or have ever heard of that you can do with a Foredom or Dremmel that is in any way beneficial to any ancient coin ever. High RPM's is the opposite of control. So, put down the power tool, step away from the defenseless coin or artifact and take ten deep slow breaths.
Hand Cleaning: Hand Cleaning or tool cleaning is one of the best ways to clean ancient artifacts, particularly coins. Hand cleaning is the process of cleaning a coin or object by sharpened instruments with the aid of a magnifying tool. The ideal setup is a binocular microscope and light source and an assortment of steel, plastic, glass, and wooden tools fashioned for cutting picking, and probing. The reason this technique is desirable, is that it gives the maximum control in applying appropriate techniques to appropriate areas on the surface of the artifact, according to the conditions of the surface. This is always desirable over global techniques which apply uniform indiscriminate processes to the entire surface of the object.
The reason I have placed this technique near the bottom of the list with the potentially destructive ideas, is that without lots of practice, you can do a whole lot of damage to a valuable coin with a sharpened blade with just a slip. Geta just doesn't look nearly as handsome without his nose.
End Part - 2 - continued in Part - 3 -
Archeology Pty Ltd, does not accept any liability or responsibility for any outcome or end result achieved or attained by using or following any or all directions contained in this eBay guide. This information is provided on the basis of good faith and use of any or all information is completely at the readers/users risk. Remember, this is a general guideline and should not be applied without testing and adequate safety precautions.
Restoration of Bronze & Silver Antiquities Part (2) Two
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20 December 2005
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