Imagine you have just spent a pleasant afternoon searching a Civil War site and were lucky enough to recover a pair of buttons, a badly corroded belt buckle and a very rusty bayonet. Once your elation fades you may begin to wonder just how you should go about caring for the items you have found. Anyone who uses a metal detector will eventually find an item that is an advanced state of decomposition. There is not always a cut and dried answer to what may be the best and easiest method to preserve a find, but the following information should help.
Iron is a good place to start. Many items high on a collectors list are made from this durable metal. Unfortunately, burial of any iron item immediately begins its decay.
Iron, when exposed to moisture, will form rust on all exposed surfaces. This process will continue until the base metal is completely reduced, so the odds of finding a really old iron object are not good. Objects of more recent manufacture may be found in various conditions. It is important to protect an iron object soon after its recovery, as exposure to more moisture in the air will speed its deterioration. All dirt and rust must be removed from the object with a wire brush or steel wool. A commercial rust remover containing phosphoric acid may be used. It should be noted that all cleaners will cause a small amount of etching or pitting, so this should be considered. Be sure to follow the manufacturer's directions and safety precautions.
Once the object is cleaned all moisture must be removed. One means of this is to soak the object in an alcohol bath, allowing it to dry well afterwards. Alternately, the object can be baked in an oven at a high temperature. Do not use your kitchen oven to do this after treating the object with chemicals! Once dried, the object should be sealed against further deterioration. If in good condition it can be primered and painted, using an appropriate type of paint.
If the object is in an advanced state of decay it should be sealed against further contact with air. A clear, synthetic plastic spray may be used to coat it or, if the object is small, the entire piece may be sealed in a block of clear casting resin. This is available at most large hobby and craft stores. The object is placed in a mold and completely covered with the resin, which then hardens into a protective block. It should be noted that this can become expensive as the resin is not cheap. A good way to check to see if an object has been totally reduced by rust is to hold it next to a magnet. If there is no attraction then the object is totally converted. Anything this far gone is beyond the scope of an amateur to repair. If you feel it should be saved, consult a conservator at a large museum for help.
Remember, as you work with a rusted item, that any tool or cleaner that can remove the rust can also affect the metal beneath that you are trying to save, so proceed slowly and with caution.
Tin objects are naturally corrosion resistant. They are often found in a damaged state due to their thinness. They may be cleaned in the same manner as iron objects. Tin will scratch easily so care should be used when cleaning. If a tin object is flattened or bent it can be gently pushed back into shape by hand, or by using a small rubber mallet or rounded punch. Work slowly and do not apply too much force or the metal will tear.
Copper and its two alloys, bronze and brass, are sometimes found. Copper can be used in its natural form, either hammered into tools or ornaments, or by casting. Bronze is an alloy of copper and tin, being about 10 percent tin. Brass is an alloy of copper and zinc. Copper can turn green; this is caused by verdigris. A tooth brush and a commercial copper cleaner can be used to remove this. Steel wool or abrasives will scratch copper so do not use them. Dents can be removed from copper items. A solid, rounded object should be used for a base. Place the object to be repaired over the base. Use a small hammer wrapped in cloth to gently tap the object back into shape. Bronze should be cleaned with soap and water only. Repairs should not be attempted, as you may damage the object further while attempting them. Brass pieces should also be cleaned with soap and water. If the object is dull it may be cleaned with acetone, then rinsed with water. A commercial brass cleaner can be used to remove corrosion and to polish the object. This may require many applications. Finally, the piece may be coated with a clear metal lacquer. Brass is very hard and repairs should not be attempted.
Pewter is an alloy formed mostly of tin and will not rust. Objects made of pewter may be cleaned with soap and water and a soft brush. Due to the softness of this alloy it will often be recovered in a damaged state. It can be repaired as copper. Use a rounded base, a cloth wrapped hammer and gently tap out any dents. Modern pewter looks like silver and may be cleaned with a silver polish.
Silver items are very soft and may bend easily. Sterling silver is 92.5 percent silver and 7.5 percent copper. Some base metals are electroplated with silver; this process began in 1840. Tarnished silver items should first be cleaned with soap and warm water and then rinsed and dried with a soft cloth. A commercial polish or cleaner should then be applied with a soft cloth. All of the polish should be removed and then the object should be washed and dried again. Damaged silver items can be repaired, but only the simplest of jobs should be attempted. Dents can be removed with a rounded base and a light wooden mallet. Never treat silver items roughly! Bent items can be gently straightened, etc., but anything more complex should be turned over to a professional.
Gold items are usually soft and should be handled with care, mainly because any object will be very valuable. Gold is alloyed with either copper to make red gold or silver to make white gold. Gold is denoted in carats, each number of carats representing how many parts out of 24 are gold in that particular item of fashioned gold. Gold suffers very little from corrosion and requires no treatment to preserve its finish. Damaged objects should be taken to a jeweler or goldsmith for all repairs.
Aluminum items are rarely found, but a quick description of them is included. When the outer surface of aluminum corrodes it forms a protective layer of aluminum oxide. This layer acts as a skin that protects the metal underneath and should not be cleaned or removed.
Glass objects such as bottles are easily restorable as long as they are found unbroken. Even if broken they may be valuable enough to warrant collecting and reassembling the pieces. Sediment and dirt inside the bottle may be removed with a wire or small screwdriver, toothbrush, etc. When bottles are first recovered they should be soaked for several days to loosen all dirt and stains. Soap and water, sink or toilet bowl cleaners, etc., can be used to remove stubborn stains. Always rinse the bottle thoroughly before using a stronger cleaning agent and do not mix them. A vigorous shaking with the bottle full of cleaning fluid also helps. Mildly damaged bottles can be repaired using clear casting resin. It can be used as a glue to reattach broken pieces, or as a protective coating on the bottles exterior. Holes or chips can also be repaired by using masking tape around the damaged area to form a mold. This is filled with the resin, allowed to dry and then sanded to form with a fine sandpaper. A very thin layer of the resin on the outside will seal the repaired area.
Recovered objects such as knives or pistols that have wooden components require special attention. If at all possible, the wooden pieces should be separated from the metal component so that they can be treated separately. Of course, this will not always be possible and under no circumstances should you risk damaging the item. If the wood is still in fair condition, all dirt should first be removed. Use a soft sponge and warm water to gently clean the item, being very careful not to damage it. Do not soak the item, keep the sponge fairly dry. Mineral spirits may be used, but be aware that they may remove the original finish. Once clean, be sure to thoroughly dry the item. There are commercial products available to restore rotted or damaged wood that may help with seriously damaged pieces.
Guldbeck, Per E., The Care of Antiques & Historical Collection, AASLH Press, 1972.
Johnson, Lorraine, How to Restore and Repair Practically Everything, Penguin Books, 1990.
Munsey, Cecil, Collecting Bottles, Hawthorn Books, 1970.