Conservation-restoration of bone, horn, and antler objects involves the processes by which the deterioration of objects either containing or made from bone, horn, and antler is contained and prevented. Their use has been documented throughout history in many societal groups as these materials are durable, plentiful, versatile, and naturally occurring/replenishing.
While all three materials have historically been used in the creation of tools, ceremonial objects, instruments, and decorative objects, their individual compositions differ slightly, thus affecting their care. Bone is porous, as it is a mineralized connective tissue composed of calcium, phosphorus, fluoride, and ossein, a protein. Horn consists of a keratin sheath over a bony outgrowth, as seen with cows and other animals. Antlers are a reoccurring bony growth on the skulls of male members of the deer family (apart from reindeer/caribou, in which both males and females produce antlers.) Unlike horn, which is a permanent feature, antlers are typically shed and regrown each year.
While these materials have a well-documented past as sturdy and reliable choices for tools, decoration, ceremonial objects, and more, they are organic materials that deteriorate if not treated properly. Deterioration may occur if objects made from these materials are subjected to extreme heat, dryness, moisture, or a combination of heat and moisture due to their highly porous nature. Other sources of deterioration include pests, acids, and overexposure to light. It is highly recommended that a conservator be contacted if a museum has bone, horn, or antler objects in need of conservation, as many adhesives, liquid cleaners, and protective coatings may irreversibly damage the object.
Identification and composition
Many museums contain objects in their collection that are made of bone, antler or horn. One of the most important steps in the conservation of these objects is determining which material it is.
Bone
Bone, which has a very similar chemical make-up to ivory, consists of inorganic materials which provide strength and rigidity and organic components that provide the capacity for growth and repair. Unlike ivory, which has no marrow or blood vessel system, bone has a spongy central portion of marrow from which extend tiny blood vessels; bone is therefore highly porous. Bone is also made of both mineral and carbon-based materials; the mineral-based are calcium, phosphorus, and fluoride; the carbon-based is the protein ossein. Bone also includes the mineral hydroxyapatite, "A calcium phosphate mineral which forms a hard outer covering over the collagen and protein matrix," or organic material.
Bone housed in museum collections come from many different sources; mammals, fish, birds, and in rare cases humans may all be included in a museum's collection. Bones in these collections can come in many shapes and sizes. It can be used in its natural form or polished with sand and other abrasives to create a smooth, glossy surface. It may also undergo a burning process, which gives it a blue-black to whitish-gray color.
Bones of all kinds have been used to create many different objects throughout history, from tools such as hammers and fishhooks to weapons such as spears, arrows, and harpoon points, or other items, such as pendants, hairpins, gaming pieces, musical instruments, and ceremonial objects.
Antler
Antler, a modified form of bone, grows out of the skull bones of certain species of animals, such as deer, and is typically shed once a year. It consists of a thick layer of compact bone, an inner section of spongy bone, and internal blood vessels that are less and more irregular than the ones present in bone. Antler is denser and heavier than skeletal bone and differs from skeletal bone in its external appearance. Skeletal bone is usually smooth except for areas of attachment to muscles, tendons, and ligaments, while antler generally has raised bumps and protrusions across the surface.
Similarly to bone, antler may be used in its natural form, polished with abrasives for a glossy surface, and treated with a burning process for a charred finish and color. Antler has been used for numerous objects throughout history including tools such as hammer batons, knife handles, pressure flakers, and conical arrow points.