Preservation is an action in order to prevent, stop or retard the process of deterioration of the Artifacts.
It is sometimes supplemented by the restoration work, which means the treatment of objects with necessary corrections and alterations.
The concept of conservation is the ultimate reality, which includes both preservation and restoration. Now the question is what do we mean by deterioration. Deterioration is the alteration in an object, produced by the interaction between the object and factors of destruction.
In dealing with artifacts pre-historians count two factors mainly:
(a) How much an object has been mechanically rolled or weathered.
(b) How far chemical changes have taken place to alter the composition of a specimen.
Stone is the first material that was used by men for making tools, implements and some other objects of daily use. During the interglacial period, when huge ice sheets melted and flowed in the form of rivers, most of the artifacts of the primitive men swept away under the current. These artifacts show the mark of mechanical rolling by the action of water. They were either dragged in a stream or hurled on towards the beach.
Whatever may be, for the friction, the edges between the facets got rounded. Some soft stone tools like flint tools became so much eroded that they look like a pebble. More fragile materials e.g. bones rarely survived under such rolling. Therefore, the tools collected from open stations often suffer from severe mechanical erosion unlike the tools obtained from a cave or rock-shelter.
In fact, a specimen cannot escape from damage when it travels a long way. Other specimens of the same age may show little or no damage when stored in a pit deposit. For this reason, a worn specimen must not always be considered older than a relatively fresh specimen. It is a very relevant point to be remembered. Because an industry is generally examined on typological ground where older tools show a greater degree of weathering than those of the later date.
In case of chemical changes, the surface of the tools, especially of flint tools shows patina. Patina is the resultant of chemical weathering. All the sides of a tool do not necessarily show the same extent of patination. The exposed parts of the tool exhibit greater degree of patination than the unexposed parts.
Another type of change, incrustation occurs in certain cases. It is a surface manifestation; not a chemical change. Different close-by materials get fixed on the surface of the tool due to prolonged exposure in nature. Besides, tools of bone and antler undergo special kind of chemical weathering.
The organic materials associated with them disappear with time and only the mineral substances persist. Bones in this condition normally become fragile but sometimes when they get fossilized, the organic matter is replaced by minerals and the whole bone becomes stone like, though the cellular structure or the general shape is retained.
Preservation protects the tools from farther damage. So they can be used for some special purposes in future:
i) Pre-historians study them carefully with a long time. They are the indispensable materials of research as valuable inferences in prehistory are drawn on them.
ii) The typo-technology of the tools is often compared with newly discovered tools.
iii) The tools may be utilized as laboratory specimens so that the students of prehistory can get their basic practical orientation.
iv) The tools may serve the curiosity of lay man who tend to acquire a firsthand knowledge about the early culture in a museum.
The stone objects disintegrate at times; the various layers fall apart. Therefore, a prolonged treatment in laboratory is required to restore them back to a sound condition. Some stone objects are found to be covered with microorganisms, which gradually tend to destroy the object. In this case treatment is needed to remove the microorganisms and to cure the object.
Besides, stone objects are subjected to various other forms of deterioration. For example, presence of salt can cause damage. Because, salt, by absorbing moisture, turns to salt solution which percolates into the cavities between the particles forming the rock. On evaporation, salt solutions turn into salt crystals, which often appear on the surface of the stone in the form of white efflorescence.
Continuous dissolution and crystallization of the salts result in the repetition of strain on stone, the surface of which ultimately turn into powder. Therefore, all stone objects, after initial analysis and interpretation, should be washed thoroughly in repeatedly changed salt-free water to drive out the salts.
Stone sculptures often accumulate dust, dirt and stains. Loose dust can easily be brushed off. Plain water can wash away most types of dirt accretions. Sometimes mild detergent in water produces better result. Acids, howsoever dilute, should never be used to clean the stone objects, except by a trained conservator who understands their action on various types of stone.
A deposit of moss or algae may be seen on stone objects, especially on those, which have remained in the open area for sometime. Such a deposit imparts a patchy, green or black appearance to the object. It may also produce pits in the surface of the stone that weaken the structure. A trained conserver is able to remove the moss deposit quite easily by the application of chemicals.
Stone objects often suffer from damage during storage, especially when big and small objects are dumped together. Some objects may break, others get abraded. Therefore, it is wise to store the objects on separate shelves or platforms. These shelves or platforms should be amply padded and strong enough to support the weight, especially in case of stone sculptures.
Clay vessels and other utensils, beads, toys, figurines etc. have been excavated from many sites of ancient culture, in different parts of the world. Clay was certainly an important discovery among man’s earliest discoveries of natural materials. Unbaked clay objects are very fragile.
They get easily affected by water and so cannot be cleaned with any aqueous solution. Such objects should be kept in a dry atmosphere. In case of painted clay objects also, water or humidity gives a detrimental effect. But the clay objects that were once baked can be washed with distilled water to remove the salts present on them.
The baked clay objects (produced at any degree of firing) are though more durable than those of unbaked clay objects, they too are fragile, subjected to crack or break. Many such objects break by accident, falling from a shelf or a table and slipping out from hands. Therefore, careful handling is the most necessary prerequisite for this kind of material.
Wood being an organic material is especially susceptible to deterioration. Man has used wood since the early days of Stone Age. He relied on it in the same scale as he did upon the stone. Naturally he made various kinds of weapons, objects of daily use as well as materials for art and decoration.
Although seemingly wood looks hard and durable, but in fact, it is perishable and vulnerable to varied causes of deterioration. It easily falls prey to insects and growth of microorganisms is often found in it. It gets affected by the change of climatic condition. It is combustible too.
So preservation of wooden materials demands utmost attention. Great care should be taken in storing them. The oldest wooden tool so far as recovered, is a wooden spear-point about 200,000 years old, found from a spot near London.
Ivory and Bone:
The use of Ivory and Bone is recognized since the Upper Palaeolithic period. They have been used in making tools, ornaments, weapon handle, beads, etc. Ivory from elephant tusks was the most common one, but walrus ivory was also recovered from North of Europe. Like other organic materials, both bone and ivory are susceptible to heat and humidity.
They expand under high humidity and contract in low humid condition. Therefore, cracks often develop in these materials. But the effect of the climate can be minimized if the objects are coated with a water-repellant substance. Both ivory and bone can be easily stained because they are porous in nature. For the storage of these objects, clean soft tissue papers must be used and finally the objects should be kept on padded shelves or in padded boxes.
Apart from gold and silver, much copper, bronze and iron objects have been discovered as exhibits of Bronze and Iron Age. Copper and its alloys, like bronze or brass, corrode easily especially when buried in the earth. Corrosion takes place as the soil contains many salts.
However, the corrosive layers of its chloride cover the upper surface of the copper object, rendering the metal friable and weak. High humidity accelerates the process of decaying. At present a preservative coating solution is available which can be applied on copper, bronze and brass objects.
Since iron objects rusts easily in moist climate, excavated iron objects are often rusted, sometimes to the extent that no or very little metal core is left in the object. If an iron object is already corroded, it should be treated in the laboratory before preservation.
Sometimes rusting is so advanced that if it were removed, the whole object or its important portions would be lost. In that case, the rust is also conserved along with the object. Formation of the fresh rust can be prevented, to a large extent, by the application of a water-repellant of its surface. The object is either immersed in wax or wax is applied on it with a brush. Beside wax, some consolidants and varnishes may also be applied on the objects.
Environment plays a major role in the conservation of artifacts. Changes in temperature and relative humidity are particularly important. Since objects remain buried for a long time, they are conditioned by the natural environment.
After excavation when they are carried to a new environment, the equilibrium gets distorted and as a result the artifacts may swell, shrink or warp. To avoid all these, perishable objects recovered from an excavation should be kept in a similar environment until they are taken to a conservation laboratory for specialized treatment.
If an object comes from a salty ground, that remains liable to much damage. In this case, immediately after the recovery, objects (pottery or organic material) should be washed thoroughly in the salt-free water. This prevents the soil crystallization on the surface of the object for which disruption could have taken place. However, the preserved articles too need protection against light, heat, moisture, mold and insects.