The marine environment provides some of the most favorable conditions for the conservation of archaeological objects, as seen in many INA Newsletter issues. Appearances can be deceiving, however, and an object that seems intact when uncovered on the seabed can disintegrate before it can lifted to the surface. In 1987, we faced just such a situation with some of the copper four-handled ingots from the Late Bronze Age shipwreck excavated by INA at Ulu Burun, Turkey.

During the 1984 through 1987 excavation seasons, archaeologists raised 70 ingots on the upper part of the wreck intact and in excellent condition. But at the end of the ‘87 season, we discovered that ingots in the middle rows were in a much poorer state of preservation, crumbling to bits as archaeologists chiselled them free from the seabed. Embedded in sand and a black, mushy, possibly organic substance, the lower ends of these ingots suffered an accelerated attack on the metallic copper. Affected areas now consist of a hard outer crust of marine concretion and copper corrosion products over a soft, black corroded copper interior. If the outer crust is broken--often the case, as rock-hard concretion surrounding each 25-kilogram ingot can require forceful chiselling--the inner corrosion floats away, leaving an empty, broken shell of concretion. In some cases, the outer crust is not even preserved, and only a discolored shadow suggests where metal once existed.

Because this deterioration was causing us to lose a considerable amount of information, we wanted both to protect these fragile ingots in place before chiselling them free and to somehow turn the "shadows" into solid casts that could be brought to the surface and studied. In other words, conservation of these ingots had to begin underwater, not on the surface in a laboratory.

In the spring of 1988 1 took on this problem as a research project in Dr. Don L. Hamilton's Texas A&M University course, The Conservation of Materials from Underwater Sites. I tested various compounds in the laboratory in several ways. In addition to rating their ability to set and adhere in salt water (using aquarium salt solutions) and to create a detailed cast or provide a strong consolidating jacket--whichever each ingot required--I wanted to be able to remove the compounds without damaging the ancient artifact. Since few conservators or archaeologists have to deal with this problem, I had to seek appropriate compounds to test in reports from fields as diverse as medicine, plumbing, oil drilling and dentistry.

Archaeologists on the 16th-century A.D. Basque whaling ship in Red Bay, Labrador, Canada, successfully used polysulfide rubber to mold ship fastenings and other features of the hull. But its low viscosity made it unsuitable for the conditions of the Ulu Burun wreck: polysulfide rubber would easily run out of the nearly vertical ingot molds, many of which also require pouring "uphill." In addition, the great flexibility of the set compound prevented it from imparting any jacketing strength, so it was rejected.

Another material applied successfully both on land and underwater is a resin-impregnated bandage used in the medical profession for making limb casts. Both 3M and Johnson & Johnson make similar products, Scotch-cast and Deltalite, respectively. Laboratory testing of Deltalite showed that it set to make a stiff, strong jacket that did not adhere to the object at all. This characteristic would be ideal for lifting pottery and complicated objects on land sites, but our conditions demand no gap between ingot and jacket. There must be intimate contact so that if any parts of the ingot should crumble during chiselling or lifting, they will be held in place by the jacket. Deltalite and Scotch-cast are also expensive and somewhat messy to use.

Some low-viscosity epoxies were tried in the lab, but these either dispersed too easily, were not viscous enough to stay on a sloping or underside surface, or did not set in a reasonable amount of time (or at all), and so were unsuitable for the task. I also experimented with a thick, fiberglass car body filler, but it did not adhere well underwater and was messy to work with.

Regular gypsum plaster of the type used in building construction or a finer type used in dental casting was one of the most promising candidates, not least of all because it is inexpensive and easily available in Turkey. Lab results were excellent: to the disbelief of many, plaster does set fully underwater to form a strong, adherent coating which can be removed easily when necessary by careful chiselling. Plaster coated gauze bandages are often used to lift fragile objects on land sites, and this seemed most appropriate for the Ulu Burun ingots.

Although plaster seems the ideal compound to use underwater, it is also brittle and slowly dissolves in water after setting. I feared that if used alone as either a molding or jacketing material, it could break apart during chiselling even if strengthened with gauze bandages. So I continued my search for a strong, more resilient compound.

A telephone assistant at the major conservation supplier, Conservation Materials Limited in Sparks, Nevada, provided me with an excellent suggestion: a two-part underwater repair putty made by the Devcon Corporation (Danvers, MA). Devcon's Wet-Surface Repair Putty turned out to be the best material tested. It adheres well to the ingot surface for jacketing, is viscous enough to manipulate easily and stay in place either on the surface or particularly in difficult-to-reach corroded cavities, has a long working time, and produces a detailed cast.

Other epoxy putties-Milliput, Sylmasta, Brookstone, Pliacre--either did not adhere at all, were not easily worked, or set to a rock-hard consistency that would have been impossible to remove from the ingot without damaging it.

Since the Devcon epoxy putty and the plaster performed most successfully in the lab, we tested their application in actual field conditions at Ulu Burun in 1988. I found the Devcon to be a pleasure to work with underwater. It can be pushed into uphill cavities and spread over surfaces very easily. Its only disadvantage is stickiness, which can be partially overcome by mixing five to ten minutes before diving so that it reaches a more viscous, less sticky consistency, and also by applying with quick pressing motions, using minimal finger contact. We used the epoxy to fill a corroded cavity on one four-handled ingot, left on the seabed over the winter to be inspected a year later.

Trials with the plaster in 1988 were less successful initially, but infinitely more humorous. Despite trying several different ways to get the plaster to the seabed, I remained frustrated by results. Plaster mixed on deck and taken down in polythene bags set by the time I reached the bottom. Plaster mixed underwater in the telephone booth, our air-filled dome anchored on the bottom for safety, set almost instantaneously. Gauze bandages dipped in plaster prepared on deck were difficult to work with underwater and often set before I got to the bottom, particularly if the dive was delayed at the last minute because of a blown 0-ring or forgotten weight belt.

Finally, the most successful method found was to take the plaster down as a dry powder in two well-sealed polythene bags. On the bottom, the bag of plaster remained dry although the high pressure caused it to feel rock hard. When ready, I cut open the bags with my dive knife, and the plaster mixed immediately with seawater to form a warm, powdery mush I could spread on the ingot surface with my hands. When there was no current, visibility all around me was reduced to nearly zero; being both blinded and affected by nitrogen narcosis, I was continually amazed that the plaster made it onto the intended ingot surface at all.

The 1988 season was primarily one of experimentation. Over the winter, 50 pounds of the Wet-Surface Repair Putty were purchased from Devcon, with a generous reduction in its cost made possible by Mr. John Pence. In 1989, underwater application began in earnest. It was still another season of experimentation in many respects as I worked to refine the technique of applying the epoxy and plaster in appropriate combinations depending on the problems presented by each ingot.

The best methods of use for different situations have been determined, but we are continuing to evaluate our techniques. For ingots missing large areas or with areas surviving only as crusts and shadows, I fill the open molds or shadows with Devcon, building it up to replicate the shape and thickness of the lost metal. The molded area adheres well to the crust and to the remaining metal of the ingot if all of the corrosion is completely cleaned out; this is the most time-consuming aspect of the work.

The repaired section and a large part of the solid metal is then coated in a thick layer of plaster, and more epoxy if necessary, to ensure that the join between the epoxy and the metal does not fail as the ingot is chiselled free. Chiselling is done as carefully as possible, using both short, thick cold chisels for the edges, and long, thin, specially made chisels to reach into the very narrow space--often less than one centimeter-- between overlapping ingots. Once the ingot is raised and stored, its plaster can be checked regularly for dissolution and reapplied if necessary.

A different process had to be devised for ingots missing small areas such as the protruding handles or "ears." I had originally filled these cavities with Devcon putty but found that cleaning out all the corrosion underwater used up a great deal of precious bottom time. Coating the thin and fragile edges with a layer of epoxy without filling the cavity permitted the ingots to be raised without damage to the surface. Once there, mushy corrosion was cleaned out more completely and a much safer bond formed with the epoxy. Also, the cavity could be filled with more aesthetic, more stable over time, and less expensive clear Araldite epoxy resin or clear Paraloid acrylic resin.