Each archaeological discovery, from the merest fragment of an object to a very complex structure, should be maintained with care, ensuring that it can be admired and studied by future generations. This is a generally accepted premise, but of the considerable amount of material buried in antiquity, only a fraction survives. What does survive can be said to have achieved an equilibrium between itself and its environment: when excavated material is exposed to atmospheric conditions different from those to which it was accustomed, its equilibrium is upset and, if no care is taken, the material will eventually disintegrate. Some archaeological discoveries are portable and can be lifted and transferred to a safer location for conservation and study. Others (i.e., remains of built structures) cannot be moved and must be treated and protected in situ.
Classified into organic and inorganic, recovered portable objects are crafted or otherwise produced in a variety of materials.
Leather, bone, ivory, wood, and textiles are among the organic materials that rarely survive. When they do, their condition is usually fragmentary and very fragile. Organic material buried under favorable conditions—in permanently dry, wet (as a bog), or freezing circumstances—has the best chance of survival. For example, if an ivory object excavated from damp soil dries quickly, it will crack or warp. [See Bone, Ivory, and Shell; Textiles.]
Objects out of stone, terra cotta, metal, and glass are more resistant to decay than those out of organic materials, but, for example, if a stable, dry bronze object gets wet, it will begin to corrode. [See Metals; Vitreous Materials.]
When an object of any kind is found in the field, it must first be protected so that the equilibrium that existed between it and the environment will not be radically disturbed. Before it is removed from the ground, however, photographs must be taken of it in situ, so that its exact position, condition, and relationship to its surroundings are recorded. This information will be useful to the laboratory conservator and restorer. How carefully an object is removed from the ground increases or diminishes the success of the available preservation techniques that can be used on it in the laboratory. [See Recording Techniques; Restoration and Conservation.]
An artifact, whether it is recovered from an archaeological excavation, survey, or rescue operation, or it is a chance find (see below), must be lifted and transferred for treatment and protection. When it is not possible to lift an object in one piece—as with a very fragile artifact or one that is not flat (e.g., a skeleton or a rhyton)—the block-lifting method is recommended: the object is lifted together with the soil that surrounds it (in a “block”) and is then transferred to the laboratory for treatment. If an object needs consolidation before it is lifted, it must be cleaned well, in situ, using the least possible quantity of consolidant, which subsequently often will have to be removed in the laboratory. An emulsion will be needed, for example, when the object is damp and needs consolidation. In any case, when used, the consolidant must be allowed to dry before the object can be lifted.
The packaging, transfer, and storage of objects found in the field are also components of field conservation. Their objective is to keep the artifact in a stable condition until it undergoes conservation treatment in a conservation laboratory.
Built structures, usually out of stone, brick, mud brick, wood, or some combination of these materials, are stationary artifacts. Because wood is an organic material that survives only under very favorable conditions, “building material” usually refers to stone, brick, and mud brick. Secondary materials used in construction are mortar, fresco, and mosaic. [See Wall Paintings; Mosaics.] All of these materials must be protected immediately upon discovery, and on a long-term basis must be protected against weathering (Price, 1984).
Conservation complications begin in the field, when important late remains are built on top of earlier ones that also need excavating (Sease, 1992). Ideally, the latest structure can be transferred as intact as possible to a nearby location. However, an excavation's budget and intentions toward protecting the site, structures, and artifacts may be incompatible. Thus, moving a structure is rarely practical because of lack of funds, space, or personnel or because its building material is in reuse (belongs to an earlier period) or the existing structures were used in more than one period. When, however, a built structure is to be dismantled or transferred, photographs, drawings, measurements, and other documentation must be made before it is disassembled, and its individual stones must be numbered for re-placement.
When the last layer to be excavated is exposed, it must be protected immediately, as must its portable discoveries (see above). It is best to build a shelter for it. Some opposition to this method exists, based on the argument that a shelter will disturb the environment. If, however, the shelter or roofing is compatible in material, shape, and color, it has a better chance of being accepted (Getty Conservation Institute, 1991).
Features associated with structures, such as mosaics or frescoes, should be sheltered within the structure. If there is no danger of theft, all should remain in situ. Otherwise, they must be lifted and transferred to an otherwise protected location.
When a site is of archaeological, historical, ethnic, religious, or touristic interest and will likely draw many visitors, paths should be built to protect both the visitors and the site. When a site is discovered accidentally and excavation is either postponed or initiated but then halted, or if a site is isolated and protection against theft or weathering may not be possible, full recording procedures should be followed, including photographs and drawings. The site should then be backfilled, including using geotextiles, a patented synthetic substance, separating the finds from the fill. In a rescue excavation the only option is usually to remove structures, after documenting them as completely as possible. Only rarely will it be possible to transfer them to another location.
- Dowman, Elizabeth A. Conservation in Field Archaeology. London, 1970. Deals with newly excavated finds.
- Hodges, Henry, and Miguel Angel Corzo, eds. In Situ Archaeological Conservation: Proceedings of the Meetings, April 6–13, 1986, Mexico. Marina del Rey, 1987. Deals with the in situ conservation of different materials.
- Price, N. P. Stanley, ed. Conservation on Archaeological Excavations with Particular Reference to the Mediterranean Area. Rome, 1984. Collection of essays on the treatment and protection of excavated finds: mosaics, stucco, mud-brick structures.
- Sease, Catherine. A Conservation Manual for the Field Archaeologist. 2d ed. Los Angeles, 1992. Excellent manual for field conservation.
Getty Conservation Institute. The Conservation of the Orpheus Mosaic at Paphos, Cyprus. Marina del Rey, Calif., 1991. Describes the process of rolling, treating, reinstalling, and protecting a mosaic with a specially designed shelter.