The conservation and restoration of ivory objects is the process of maintaining and preserving objects that are ivory or include ivory material. Conservation and restoration are aimed at preserving the ivory material and physical form along with the objects condition and treatment documentation. Activities dedicated to the preservation of ivory objects include preventing agents of deterioration that specifically connect with ivory as a material, preventative conservation, and treatment of ivory objects. Conservators, curators, collections managers, and other museum personnel are in charge of taking the necessary measurements to ensure that ivory objects are well maintained and will make the decision for any conservation and restoration of the objects.
Ivory as a material is the tusk or teeth from animals and is soft and malleable with nonmetal tools. Often used in decorative and practical objects, ivory can be inlaid and used as an accent within objects made from other material like metal and wood. A popular decorative ivory work is scrimshaw, which is etched ivory with black or colored pigments. Ivory has been manipulated since prehistoric times and as a material has been used in religion, as jewelry, piano keys, decorative arts, and other products. The demand for ivory has caused specific animals to become endangered, including the African and Asian Elephant. Ivory is a coveted material throughout Europe, Africa, and Asia that is illustrated in religious objects, art, and demonstrates wealth. In the last thirty years, ivory has been mainly been used in the jewelry and souvenirs markets."To Save An Elephant" by Allan Thornton & Dave Currey, Doubleday 1991
Ivory
Ivory is the tusks and unusually large or projected teeth of animals, such as elephants and walruses. It consists of dentin and made up of both organic (for growth and repair) and inorganic (rigidity and strength) components. Due to it being organic and inorganic the ivory is extremely sensitive and reactive
Types of ivory
Understanding the diverse types of ivory is important as it can impact the type of conservation and restoration work that is done. It can also determine the materials that are harmful or safe to use on the ivory.
Elephant and mammoth
Elephant and mammoth ivory comes from the two modified upper incisors. Tusks of some male African elephants can grow up to 2 meters (6 ½ feet) and weigh up to 45 kilograms (100 pounds). The tusks have a pulp cavity where the root and soft tissues attach to the jaw and that extends for approximately one-third of the tusk. By looking at if the carved ivory does or does not have the pulp cavity it can help indicate what part of the tusk was used and its original length.
The characteristic identifier in elephant ivory is the pattern of intersecting arcs that can be seen in the cross-section. These arcs can go by several names such as engine turnings, cross-hatchings, or Schreger lines (named after the German anatomist who first described them in 1800). The intersections of the lines form angles, obtuse arc angles are found in elephant ivory and acute arc angles are found in mammoth ivory.
Walrus
Walrus ivory is solid its entire length with a center of secondary dentin instead of a pulp cavity. It is characterized in cross section by the central core that has a marbled appearance surrounded by the smooth creamy white dentin layer. They may grow up to 1.0 meter (3 ¼ feet) in length.
Warthog
Warthog ivory comes from their upper and lower canine teeth and are strongly curved. It generally has squared cross sections and have a mottled appearance. When using a magnifying hand lens, the wart hog dentin shows irregularly spaced concentric lines with varying thickness.
Narwhal
Narwhal ivory comes from a single left incisor that is produced by males. It is distinguished by its spiral form. They can grow 2.0–7.0 meters (6 ½–23 feet) in length.
Hippopotamus
The upper and lower canine and incisors are the most common sources for hippopotamus ivory and each one has a distinctive gross morphology. Using a magnifying hand lens, we can see tightly packed series of fine concentric lines, which can be regularly or irregularly spaced. The orientation of these lines will follow with the overall shape of the tooth. Hippo ivory is harder and opaquer than elephant or walrus ivory.
The upper canines are curved and are oval to rounded in the cross-section. The lower canines are the largest teeth and strongly curved. In their cross-section, they are triangular. The incisors can be described as peg shaped and the center of the tooth in the cross-section shows a small dot.
Sperm whale and killer whale
Both the sperm whale and killer whale have conically shaped teeth with a small amount of enamel at the tips and the rest of the tooth covered by cementum. The cross-sections of the teeth are rounded or oval. A characteristic feature is that the dentin forms in layers that alternate directions giving it a banded appearance. Their teeth are second in hardness to hippopotamus ivory. Sperm whale teeth may grow up to 20 cm (8 inches) in length while the killer whale teeth are slightly smaller. Killer whale teeth show two slight peripheral indentations and may also display a faint rosette pattern in the dentin cross-section.
French ivory
French ivory is a synthetic material that is typically composed of pigmented cellulose nitrate and/or casein. This type of ivory was commonly made in the late 19th century and early 20th century. It looks like elephant ivory and can have intersecting line patterns but the pattern is more uniform and regular than natural ivory. This ivory will be occasionally marked synthetic while "French Ivory" or "India Ivory" are common marks. It can be distinguished from natural ivory due to its lighter weight and more even coloring.
Cellulose nitrate can be identified with a chemical spot test using diphenylamine. This ivory can degrade and produce acidic and oxidizing nitrogen. Oxide gases have been known to spontaneously combust so if this type of ivory shows any deterioration it must be kept away from the rest of the collection.
Vegetable ivory (ivory nuts)
Vegetable ivory is derived from several dense palm nuts that are native to Africa, South America, and the South Pacific. It is a cellulosic material. They grow to a maximum of 5 cm (approximately 2 inches) in diameter.
Composite mixtures
Can be various mixtures including ivory dust and casein, ivory dust and styrene resin, calcium carbonate and adhesive, casein and hardener.
Plastic
A proprietary plastic of cellulose nitrate and camphor that was developed in the mid-19th century as an ivory substitute. Other examples include polyester and phenolic resins. The plastics are sometimes laminated to show a striated surface to resembles ivory but ivory's intersecting arc pattern cannot be reproduced.
Agents of deterioration
Ivory is susceptible to certain challenges to their preservation. In order to protect against damage, conservators should determine the agents that threaten its material make-up. The agents of deterioration include the following:
Physical forces
Ivory is very fragile and susceptible to cracking, chipping and breakage. Ivory is porous, brittle, and prone to impact damage and delamination. This can be caused by human error such as dropping, bumping, or mishandling. It can also result from improper display and storage such as unstable shelving or lack of padding.
Fire
A special caution applies to French Ivory. Because it is usually composed of cellulose nitrate, it is potentially flammable and must be kept away from heat or other sources of ignition.
Pests
Bone, ivory, and antler are rarely attacked by insects, but horn is often seriously damaged by the larvae of carpet beetles and clothes moths.
Light, ultraviolet, and infrared
Ivory, bone, and antler should be kept away from bright light such as spotlights or direct sunlight. Bright light can increase the surface temperature of the object. When exposed to light, ivory can become stained or bleached, and ultraviolet light can cause it to yellow.
Incorrect relative humidity
Ivory is hygroscopic and anisotropic which means it absorbs or releases moisture with changing humidity. Ivory tends to shrink, swell, crack, split, and/or warp on exposure to extremes or fluctuations in relative humidity and temperature. Low relative humidity causes desiccation, shrinkage and cracking, while high relative humidity can cause warping and swelling.
Thieves and vandals
Ivory objects may have come from illegal trade, so it is important to know what type of ivory the object is made from and its provenance.
Water
The organic components in ivory is called ossein, which is decomposed by hydrolysis and after long-term exposure can cause the ivory to turn into a sponge-like substance. Even for cleaning purposes, water can damage ivory so it should be avoided.
Pollutants
Corroded metals and colored materials can stain ivory and should not be placed near them. Dust can be removed from ivory using a soft brush.
Incorrect temperature
Although ivory is most susceptible to fluctuation in relative humidity, it should be kept at a stable temperature that does not exceed . Ivory will warp in high temperatures, therefore extreme conditions in temperature should be avoided.
Disassociation
Disassociation is the result of losing an object or object-related data. Attempting to remove the ivory's patina or attempting to clean or repair an ivory object that is in poor condition can cause damage and lead to the loss of valuable information on the object's origins or production method.
Preventive conservation
Handling
When working with ivory objects it is important to wear white cotton gloves and if none are available be sure to thoroughly wash hands prior to touching the object. Since ivory is a porous material it is susceptible to staining. Ivory will yellow and/or brown with repeated contact to skin, fatty acids, and oils.
Temperature and relative humidity
Ivory is a hygroscopic material meaning that is absorbs and releases moisture with changing humidity. It is very reactive to its environment with the most severe changes linking to temperature and relative humidity. The relative humidity ideally is between 45–55% and the temperature at . If the relative humidity is too low it can lead to desiccation, shrinkage, and cracking. When the relative humidity it too high is can cause warping and swelling of the ivory. If the relative humidity exceeds 60% for a sustained time there is a chance that mold can develop on the ivory. It will be a white and greenish fuzzy growth that will require particular care and cleaning.
Research has found that temperature does not have as great of an impact on the condition of ivory that relative humidity does. Big fluctuations with either temperature of relative humidity is harmful. When the temperature fluctuates from normal to high heat it will cause expansion and contraction of the ivory. Elevated temperatures can also result in a series of color changes.
Lighting
Sunlight and artificial light can damage the surface of the ivory by discoloring (patina) as well as make it more brittle. Sunlit or spotlight display cases as well as any closed cases where heat can build up from interior light bulbs will cause further damage ivory. Dark storage areas will help to prevent damage to the ivory objects.
Lighting is kept at 5 foot-candles
Integrated pest management
Ivory is very rarely attacked by insects but benefits from being routinely inspected to ensure no pest activity. Rodents or other small mammals can cause structural damage by chewing on the surface of ivory. By maintaining good housekeeping and having an integrated pest management program will help prevent infestations.
Proper storage