Conservation process of archaeological materials
Paleontological laboratory studies play a key role in preparing fossil materials for the purpose of identifying and determining mammal’s evolution and chronology as well as understanding the interactions with their environment.
Therefore, securing the conservation of fossil materials before analysis is crucial for better understanding and interpretation of the anatomy and morphology of the bones. However, considering the fragile nature of most fossil specimens, a proper conservation work is often a pre-requisite to avoid shock resilience.
During excavations, both from historical and prehistoric sites, bones or faunal remains can be found especially from burial sites, kitchen areas and naturally buried at stratigraphic levels. In Eritrea, several prehistoric sites are known mainly from the Danakil Depression of the Northern Red Sea Region. Since the inception of the projects in this region, in this locality, ample collection of faunal remains has been collected. One example of the collections is the almost complete cranium of the Buia women, dated to about one million years. Among the faunal collections from this region (mainly from the Engel Ella – Ramud Basin) include the remains of hippos, elephants, pigs, horses, rhinos, giraffes and hyenas. These fossil remains are collected during field seasons and at this time they are housed at the Archaeological Heritage Research Branch’s laboratory of the Commission of Culture and Sports. This year, practical programs concerning careful cleaning, restoration, preservation process and analysis have started. Following are the technical procedures that we use at the AHRB laboratory.
When a fossil is found exposed at a surface, the general space should be properly delimited with a small trowel and a brush. Then, after the bones are carefully excavated and separated from the sediment, they are gently cleaned using wooden and/or metallic instruments. Fragile bones have to be consolidated with Paraloid B-72 at 5 to 10% in acetone.
In order to ensure the safety of the fossil materials collected from fieldworks, they should be extracted very carefully, and placed temporarily on a support using a sediment block. After these, the surface of the material can be slowly re-sized using point iron bars, and when the material is ready it can be covered using aluminum foil. Then after, the material’s condition, measurements and photos can be taken for the purpose of documentation and analysis.
Archaeological remains are generally found covered with sediments, and are often penetrated by the roots of small plants. Sometimes, in order to remove sediment from the surface of an artifact, you can simply rinse the object in water. Well preserved bones can also be cleaned by brush, engraver machine, metal and wood engravers, small pieces of wet clothes or cotton. In our cleaning process we do not use detergents, as they may contain colorants, perfumes, and other additives that may contaminate the bone, rendering it useless for chemical analysis or dating. Stubborn dirt deposits can be gently dislodged with a paint brush or wooden probe, but this is done cautiously as wet bone can be soft and easily abraded. Rootlets growing in the bone can sometimes be removed with tweezers. But careful procedures are taken not to pull fragments of bone off with the rootlets, which are often branched beneath the surface. Some of the dirt and rootlets are removed in the field under the supervision of an archaeologist who decides on the degree of cleaning required.
Faunal (animal) remains are often damp or wet when first excavated and must be dried before they can be studied or stored in a research collection. Undeteriorated specimens of bone, antler, and ivory can be treated by a non-specialist, but deteriorated specimens may require the advice of conservator. To test hardness of the surface, we press the surface of the bone in several areas. If it compresses or feels spongy, the material has deteriorated.
First, assess the condition of the bone to determine whether the material is bone, antler, or ivory. Ivory, which has multiple layers is denser than bone or antler and is more likely to crack or delaminate while drying. Next, determine the condition of the material. One good indication of condition is the hardness, so gently press the surface of the bone in several areas. If it compresses or feels spongy, the material has deteriorated. Deterioration can be roughly divided into three categories: a hard surface indicates little or no deterioration; a soft surface with a hard bone beneath indicates slight to moderate deterioration; and an extremely soft surface indicates a high degree of deterioration. In the latter case, it may be necessary to consolidate the material.
Bone that is hard or has only a slight softening of the surface can probably be air dried safely, but bone that is soft is likely to be sensitive to water loss. However, hardness is only one indication of its condition. Some burial conditions selectively damage one or more components of the bone, leaving objects that are hard but still susceptible to damage (e.g. shrinkage, twisting, cracking, or delamination) when air dried. Therefore, even if a bone is hard and apparently durable, test dry a few pieces. If any problems are noted, a decision can then be made about consolidating the other pieces. After cleaning using paint brush, pneumatic engraver if needed, scalpel, wood materials, gauze, we consolidate the bone. The decision to consolidate must be considered carefully as consolidants can interfere with the chemical analysis or dating of the bone. The consolidation process is done by mixing acetone with Paraloid B-72, and the proportion differs with the type and condition of the bone. After applying acetone, the material needs time to dry. Drying should be slow and controlled. The simplest method is to lay the clean wet bone on a table or open mesh rack and allow it to dry slowly. Turn bones frequently to ensure even drying, and monitor all pieces for cracks, delamination, or other physical changes.
Bone should be dried at a moderate humidity and cool temperature, out of sunlight and away from any heat sources. The rate at which the bone dries can be slowed by increasing the relative humidity. If cracking occurs while drying more consolidation is needed.
Finally, throughout the lab process and after packing and storage, the bone is accompanied by a detailed and proper documentation system. All the steps of laboratory processes are properly recorded and documented. For example, all the solvents applied during the laboratory processes have to be recorded thoroughly. These documentation strategies can inform and alert researchers about the possible interference of the materials during future testing.