How to Conserve Underwater Relics
Failure to properly conserve artifacts will ultimately result in their destruction. If an artifact cannot be properly preserved, there is no point in recovering it. Steel or Iron objects will literally turn into dust if not properly preserved. Preservation is a labor intensive and sometimes costly undertaking, Partial preservation will only prolong the objects inevitable destruction and the only way to ensure the artifact further deterioration to is to follow a preservation plan similar to those listed below. These methods are some of the ways members of the California Wrecks Divers have preserved artifacts. These methods are not the only ways to conserve artifacts recovered from shipwrecks and even under the best controlled laboratory conditions, the outcome of the preservation may vary or end up with unsatisfactory results. Individuals using these methods do so at their own risk. Some of the methods require the use of chemicals which if improperly used my cause injuries. Whenever using any chemicals use caution, follow the manufacture’s recommendations, and use them only in well-ventilated areas. Wear safety equipment like rubber gloves, rubber apron, eye protection, and a respirator. The recovery of artifacts may have Federal, State, and local laws governing their recovery. The California Wreck Divers Inc., assumes no liability for following these preservation techniques, any injuries sustained from these techniques, nor any legal responsibility for the illegal recovery of any artifacts.
Unfortunately, naturally occurring electrolysis dramatically effects different metals in salt water. Certain metals react with the salt water causing a galvanic action that will completely dissolve the metal over time.
Iron or Steel
Preservation of iron and ferrous metal is an extremely difficult and time-consuming operation. All steps must be completed in order protect the artifact from deteriorating from the inside out.
During its years of submersion, ferrous metals become porous, allowing saltwater deep into the metal. Some of the metal leaches from the interior, coating the exterior with an inch or two of black, brittle corrosion. The covering can be easily be removed by striking the object with a blunt instrument such as a hammer, often revealing the object in its original form. However, the appearance is deceiving as much of the metal in the body object has been leached out and replaced with salt water. Once the object dries, the salt inside crystalizes and the object will disintegrate from the inside out, leaving behind a pile of orange dust.
Prior to preservations, all ferrous metals should be kept wet and not exposed to the air for any length of time. After all foreign matter (rust and conglomerate) has to be removed before treatment can begin. Small objects can be cleaned in an ultrasonic bath. The chemical process begins by immersing the object in a bath consisting of 10 percent nitric acid and 90 percent fresh water. This is followed by several washes in fresh water to remove all alkaline traces. To remove all corrosion and preserve the metal, there are two methods you can use; electrochemical or electrolytic reduction.
The immersion of silver in salt water quickly converts it to silver sulfide. In order to clean silver, an electrolytic reduction process should be used.
The corroded silver coin or object is connected with copper wire to the negative side of the battery (cathode) and placed between two plates of sheet iron. The iron forms an anode connected with copper wire through an ammeter to the 6 or 12 volt battery on the positive side in a glass or plastic container filled with water and a 5 percent solution of caustic soda, which acts as the electrolyte. Current passing into the bath through the ammeter may be adjusted using a variable resistor. Hydrogen is evolved at the cathode as corrosion is reduced. The chlorides are transferred to the iron anodes.
The length of the process depends on the amount of corrosion on the object and should be removed and inspected periodically until all corrosion has been removed. There will be a smaller layer of insoluble oxides or ponder which can be removed by brushing under running water. The object can then be rubbed with a paste of water and baking soda to brighten it.
Electrochemical Reduction: The object is put into a bath of 10 percent sodium hydroxide and 90 percent water and soaked form four to eight weeks, depending on size. It should be removed and placed into a bath of the same solution and this time covered with zinc chips or surrounded by zinc plates. Soon after the zinc is added to the solution, it will begin to bubble and continue throughout the two to four more weeks the object is in the bath. Upon removal, it will be covered with a white coating which can be removed by placing it in another bath of 5 percent sulfuric acid and 95 percent fresh water.
Once removed from the bath it should be placed in a running water bath for at least a week and brush cleaned several times a day. Following the water bath the object should be submerged in another bath of distilled water for at least a week. The object now needs to have the water removed form it and that is accomplished by heating it in an oven at 212 degrees Fahrenheit form eight to forty-eight hours depending on size. After this a light brushing to remove any scale should be completed before moving on to the next stage.
The final step is to seal the object from contact with air and moisture to prevent fresh corrosion. The most widely used method is a clear flat lacquer or plastic spray applied in several coats over the entire artifact.
Electrolytic reduction: This is completed using the same process described in preserving silver.
Metals: Copper, Brass and Bronze
Copper, brass and bronze are recovered in far better condition than ferrous metals and are usually easier to clean and preserve. However, if the nonferrous metal is in a large ferrous debris field, the electrolysis underwater will eat away at the nonferrous metal until nothing is left of the object. Calcareous deposits and green patina can be removed by immersion in a bath of 10 percent nitric acid and 90 percent water. The mixture will dissolve the growth and remove the patina. Washing in fresh water and finally soaking in a running water bath for several weeks to flush out the remaining salts follow this. Twenty percent Muriatic acid (common pool acid) can be mixed with 80 percent water to remove any the overgrowth in place of the nitric acid mixture.
After drying for several days, the object can be buffed with fine steel wool and a polishing agent to restore that brilliant look. Once polishing is finished the object should be coated with a high gloss clear lacquer or plastic spray to seal it from the air and moisture. This step will also give the artifact an “always polished” look and will require only occasional cleaning with a damp cloth to maintain the shine. One way to save a lot of time is to take the object to a commercial polishing company after the baths are completed. They can polish, smooth rough spots and coat the object substantially faster than you could accomplish by hand and tend to be affordable.
Wood comes under immediate attack from Teredo Worms, fungi, and bacteria. Organic material recovered from salt water must be kept wet and not exposed to the air. After all foreign matter has been removed, it should be bathed in fresh water from two to four weeks to remove all the sea salts. Change the water at least daily, but a running water bath is best. Small objects can be placed in a toilet bowl tank.
There are two methods of preserving the wood once the salts are removed. First, the object can be boiled in a solution of equal parts by weight of Alum, Glycerin, and Water. Remove the container from the heat source and allow to slowly. The object should remain in this bath from one to two days, depending on size. Once the object has hardened and air-dried, it can be coated with a solution of 50 percent turpentine and 50 percent linseed oil. The polyethylene glycol (PEG) process has also proved to be quite successful. The second method is dehydration.