The archaeological excavations undertaken in Egypt by the IEASM benefit from a conservation and restoration laboratory aboard the ship, enabling objects to be treated the moment they emerge from the water. The first stages of conservation are thus carried out on the ship, and the complementary treatments, which require heavier equipment, are carried out on land, at a laboratory in Alexandria.
Aboard the Ship
As far as possible, the removal of delicate objects requires the involvement of the conservator underwater. Nevertheless, it is on the surface that the items really begin to be treated. The object is first washed clean of sediment, then identified and inventoried. Finally, items are carefully packaged, according to the needs of the different materials. On board storage makes it possible to begin the first stage of treatment, which consists of eliminating the salts impregnating the objects. Salts are harmful to the long-term conservation of the objects; during drying, stone and ceramics crystallize, opening up fissures, buckling and causing a loss of material. For certain metals such as bronze, salts and especially chlorides cause cyclical corrosion, which can cause the complete disappearance of the metallic object. Initially, the elimination of salts is carried out by simple osmosis, by immersing the objects in rinsing vats containing fresh water which is renewed regularly. This extraction is monitored and followed by measurements of electrical conductivity.
Objects found under the sea are generally covered in accretions of sediment associated with marine organisms. These calcareous concretions, which are sometimes very thick and hard, can render the object unrecognizable and retain a large quantity of salt. In order to enable objects to be identified and facilitate the desalination treatment, a ‘surgical’ process of mechanical cleaning is carried out, sometimes under the microscope, with the aid of pneumatic micro-chisels and scalpels. This cleaning process is sometimes accompanied by a chemical treatment, as certain objects with a fragile surface cannot endure repeated vibrations and pressure. Stone objects bearing inscriptions or decorations, like the large stele, are examples of delicate objects which need such treatment.
As a general rule, chemical treatments are rarely used on the ship, with the exception of lead objects which cannot tolerate a radical change of environment. The transfer from seawater to fresh water brings about rapid corrosion and the formation of a white efflorescence. Consequently, they are conserved in a chemical solution of sodium sulphate before being electrochemically treated at the laboratory in Alexandria.
The Laboratory in Alexandria
The meticulous work of conservation and restoration is continued in the laboratory at Alexandria, which possesses a wide range of equipment capable of dealing with the numerous types of damage to the archaeological artefacts. Treatments may be mechanical, chemical and electrochemical.
The restoration of metals and their conservation is complex. Although gold, the noble metal par excellence, does not suffer any damage, bronze, silver, iron and lead are conversely subject to rapid corrosion since the emergence into the open air causes a disruption to the environment in which they had attained an equilibrium. For certain metallic objects, desalination by osmosis is not sufficient. If the internal metallic structure permits, the treatment must be completed by regulated and precise polarization of the object in a chemical solution (electrochemical stabilization treatment). Once the salts contained in the metal have been eliminated, the object’s original surface can be precisely identified by an attentive examination of the stratigraphy of the corrosion. A specially adapted treatment is then chosen in order to remove these substances selectively. The chemical solutions of various acids, bases, reducing agents or complexants are implemented. Mechanical cleaning using an ultrasound scalpel, fibreglass brush, pneumatic micro-chisel, micro-lathe equipped with diamond-tipped grinding wheel, small brush and abrasive gum completes these surface treatments, which reveal the object’s original surface. This long and meticulous work is generally carried out under the binocular microscope. The fragility of the surface sometimes necessitates impregnating it with strengthening agents. In certain cases, objects are reinforced with resin or lined with sheets of fibreglass. Metallic objects then receive a chemical stabilization with a corrosion inhibitor, before being covered with acrylic varnish and a mineral wax which protect them from the air’s humidity and facilitate their conservation in the long term. Finally, they are stored at a constant temperature and humidity in order to forestall any further corrosion.
In order to complete the desalination of ceramics, the first treatment is finalized by baths of distilled water, reducing the level of salt to an acceptable one. This value corresponds with the degradation for the object, thus enabling it to be stabilized and conserved for the long term. After desalination, the ceramics are restored: the fragments are glued back together, holes are filled in and coloured, while fragile pastes, which are unfired, are impregnated with a strengthening agent. In order to prevent any recrystallization of the salts, this archaeological material should be stored in premises with constant humidity and temperature and the environment carefully conditioned for any public exhibitions.
The process is essentially the same for statues and other architectural items made from stone. Initially, the procedure consists of chemically and mechanically removing concretions. Nevertheless, marble, limestone and sandstone require a longer desalination time than basalt or granite, which are less permeable to salts. Pieces which are damaged are consolidated by the infiltration of a reversible acrylic resin. For filling or strengthening the surface, a cement is produced by crushing stone similar to the one the object is made of and bound with a reversible resin. Where necessary, fragments of statues are pinned back together.
Organic archaeological material (wood, leather, basketry, textiles, bone, etc.) demands rapid and delicate treatment as soon as it reaches the surface. Unlike other materials, the damage to organic objects is not always visible. Waterlogged wood, for example, retains its original shape in many cases. The damage is internal and its physical and chemical properties are found to have been substantially changed. Thus, damaged wood has a tendency to become soft and spongy. As soon as it emerges from the water, it shrinks, splits and twists. The cells supported by the water collapse and the wood rapidly loses its original shape in an irreversible way. It is commonly agreed that as a preventive measure, before any drying, wood must undergo a strengthening treatment. Thus, after washing and desalination, the water which these objects absorb must be progressively replaced by a resin. This resin maintains the cells’ initial shape, preventing their collapse during drying out, which is carried out slowly and in a controlled manner.
Conservation is not the application of techniques and treatment processes but a vital stage in excavation. Sometimes, in the case of fragile objects, the conservator is the first but also the last to see technical or historic details which have been retained. Just as in an archaeological excavation, it is incumbent upon him or her to register all the information which the object conveys. This documentation, sometimes supported by analyses, is not the ultimate goal for the object, which must also be stabilized to ensure its survival, and sometimes aesthetically improved for museum purposes. The objects presented in this exhibition, which come from the port of Alexandria and the Bay of Aboukir, represent only the last stage in a long process of conservation and restoration.
Source: O. Berger, ‘From excavation to exhibition: restoration and conservation’, in F. Goddio, D. Fabre (eds.), Egypt’s Sunken Treasures. Catalogue of the exhibition. Munich, 2008, p. 282-285.
PRESERVATION OF OBJECTS FOUND IN THE BAY OF ABUKIR
The missions of IEASM in 2000 and 2001 in the Bay of Aboukir allowed for the recovery of widely varying objects such as bronzes, ceramics, potteries, various stones and extremely diverse organic materials. Conservation is the main concern of marine excavations, since objects can be severely damaged upon their return to the open air following the radical change of environment. Omitting preliminary measures can result in cracking and shrinkage, while pressure due to saline crystallization can cause considerable damage. The first concern is stabilization. Objects must be kept in a humid environment in order to avoid these types of accidents, until their transfer to the laboratory in Alexandria.
In the laboratory, the different materials are classified, while still observing the principle of minimal intervention. Classification is followed by a bath in distilled water, and then conservation report forms are created for each object, including the site, name, material, catalogue or record number, description, dimensions, photos, beginning and end dates of restoration work, as well as suggestions for further treatment, including mechanical and chemical cleaning, distilled water baths and finally stabilization (consolidation or possibly the addition of a support). Finally, the type of packaging and the storage location are noted.
Treatment begins with mechanical cleaning to remove sand, mud and marine concretions; chisels, scalpels and dental cleaning tools are used and the hard, compacted layers are removed using compressed air, small electric drilling tools or ultrasound. These techniques may be used from the distilled water phase, while maintaining the optimal salt content of 50 microSiemens for freshwater. At the end of this phase, the percentage is reduced to 30 micro-siemens, as drying procedures begin. If the object is made of metal, an ultrasound treatment is used next to remove the compacted layers, while avoiding damage to the ancient metallic layers. Once the stage of stabilization at 30 micro-siemens has been reached, the isolation process is started using BTA (benzotriazole), a substance commonly used to neutralize chloride ions that cause acid corrosion.
Next, the surface is coated with a mixture of wax dissolved in white spirit in order to protect the surface from the air. Once the objects have been completely stabilized, they are stored in a shed equipped with a monitor to maintain relative temperature and humidity at an average of 20º C and at a low humidity level, not above 40—45 %.
With pottery and glass, when they emerge from a bath of distilled water stabilized at 30 micro-siemens, one must be aware that they are very porous and must be dried slowly while being monitored closely in order to avoid cracks or other damage. Fragments are re-glued after drying, then stored.
The same steps are followed for stone as for pottery and ceramics. Algae and mould on the surfaces may be removed mechanically using pincers and a solution of calcium hypochlorite sodium carbonate. Next, they are washed in running water and left to rest in a basin of tap water until the stabilization stage at the required level of 30 micro-siemens.
Amira Abou Bakr El-Kousht
Source: Amira Abou Bakr El-Kousht, ‘Preservation of objects found in the Bay of Abukir’, in F. Goddio, D. Fabre (eds.), Egypt’s Sunken Treasures. Catalogue of the exhibition. Munich, 2008, p. 286.
C. Piffaut, L. Tamborero, ‘A Sieable Project: The conservation, restauration and presentation of the large stone objects’, in F. Goddio, D. Fabre (eds.), Egypt’s Sunken Treasures. Catalogue of the exhibition. Munich, 2008, p. 287-288.