Material Conservation: Ivory

This article was copied with permission from Megan Springate, a student in the Collections Conservation and Management program at Sir Sandford Fleming College, Peterborough, Ontario. The purpose of this series of articles is to provide information on the identification, cleaning, storage and handling of antiques and collectibles, in order to extend their life.  For more information, we suggest you visit Uniclectica Antiques and Collectibles

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Storage and Handling of Ivory

Part of the Uniclectica Antiques and Collectibles Online Series “Caring For Your Antiques and Collectibles”

Ivory is very sensitive to heat and light, as well as to moisture. When examining ivory, beware of heat from lamps, photo lights, and even your hands, especially if the ivory is thin (i.e. a veneer, or piano key). Ivory must be kept away from direct sun, heat, external walls (because of the danger of moisture condensation), cold windows, and any other source of moisture (i.e. the basement, or attic). This extreme sensitivity of ivory to changing relative humidity should be taken into consideration when it is being transported — avoid sudden changes from a dry climate to a humid climate, or transportation by air where there are sudden temperature changes. Special arrangements can sometimes be made — ask your courier.

If ivory is kept in an environment where the relative humidity is 70% plus, you can get mold and mildew damage, including black spots and etching of the surfaces.

Ivory yellows with age, and when kept in the dark (this is why the bottom of an ivory object is often darker than the surfaces exposed to light). Ivory will also turn yellow/orange when exposed to sulphur, and must therefore not be stored with keratin-based objects such as tortoiseshell (keratin contains sulphur). Also, watch out for sulpher in adhesives, building materials, rubber, paints, etc. An activated charcoal scavenger may be helpful (sew a small bag out of unbleached cotton. Fill with the activated charcoal sold for fish tank filters, and sew closed. The activated charcoal absorbs sulphur and other impurities).

For storage, ivory should be wrapped in acid-free tissue or cotton, and stored in a polyethylene bag (i.e. a Ziplock) or a closed container (i.e. Tupperware). If necessary, enclose an activated charcoal bag. By storing ivory in these closed containers, changes in relative humidity will be moderated. Make sure that any display or storage materials are colourfast! Ivory is porous, and easily picks up colour, salts, and oils (i.e. from our hands — cotton gloves are recommended when handling ivory); metal corrosion can also stain ivory.

Note that ivory becomes more brittle with age, and should be handled with care.

Identifying Different Types of Ivory

Part of the Uniclectica Antiques and Collectibles Online Series “Caring For Your Antiques and Collectibles”

What Is Ivory?
Ivory is the teeth of animals. “True” ivory comes from elephants and mammoth; however, the term is generally applied to the tusks of other mammals, and some synthetics. Chemically, ivory is similar to bone and antler, and comprises a collagen matrix with a mineral component. Unlike bone, ivory has no blood vessel system, and is therefore more dense.

The most commonly found ivories in North America come from elephant, walrus, sperm whale, and hornbill. It is possible to tell these ivories apart, as they are structurally different.

1. Elephant Ivory
This category includes ivory from both Indian and African elephants, as well as ivory from mammoths and mastodon. The tusks, or upper incisors, of these animals are used. They can have a cross section of up to 20cm (8″), and be up to 2.5m (almost 3 yards) long. They are oval in cross section, and are made up of a hard, dense tissue called dentin, which is made up of 70% inorganic material, and 30% collagen. Unlike human teeth, elephant tusks do not have an enamel coating. They do have a cementum layer, however; ivory dealers refer to this as the “bark” or the “rind”. Occasionally this layer is retained on a piece of worked ivory. One-third to one-half of an elephant tusk is hollow.

Growth occurs as layer upon layer of calcified tissue is deposited on the interior of the tusk; you can see these concentric oval growth lines (called the Lines of Owen) in cross section. If you cut ivory lengthwise, these lines appear triangular. Fine and even near the hollow of the tusk (the pulp cavity), these lines become wavy and have milky areas between them as you get closer to the outside of the tusk.

Unique to elephant ivory are the Lines of Retzius. These fine intersecting lines are visible in cross section, and give an engine-turned effect (intersecting lines with a diamond shape between them).

Generally, elephant ivory has a fine, even grain and is easily carved in all directions. It can be thinly cut (i.e. for piano keys), and can be more deltcately carved than bone. This ivory is often painted or stained, dyed, and gilded. When cut, the pores of the ivory fill with an oily substance, which helps the ivory polish up nicely.

2. Hippopotamus Ivory
This is the second most commonly used ivory, after elephant ivory. Often used for flat items, such as buttons and inlays, it comes from the lower canines and incisors of hippos. The size varies, depending on the size of the animal.

The lower canine is curved, and has a triangular cross section; the incisor is straighter, and has a circular cross section. Both have two layers of dentin: an outer, primary dentin, and an inner, secondary dentin. The innermost layer has a marbled appearance which differs by species, and can even appear to have a greenish cast. The pulp cavities of these teeth are fairly small. Unlike elephant ivory, hippo ivory does have a thick enamel coating.

Hippo ivory is denser than elephant ivory, harder to carve, and has a finer grain. There is none of the “engine turned” effect in cross section, rather, hippo ivory has concentric rings in cross section. Finally, hippo ivory is less prone to decay than elephant ivory.

3. Walrus Ivory
This ivory comes from the upper canines of walrus. It is oval in cross section, and can be over 2 feet in length. It has an inner dentin layer (which has a high mineral content; it forms as the tusk grows, and leaves a marbled look on finished objects), an outer dentin layer, and a smooth, dense cementum layer. Walrus ivory is used primarily for small objects.

4. Sperm Whale Ivory
Thirty teeth of the sperm whale can be used for ivory. Each of these teeth, up to 8″ long and 3″ across, are hollow for the first half of their length. Sperm whale ivory is easily confused with walrus ivory, as both have two distinct layers. The inner layer of sperm whale ivory, however, is much larger. As well, in a longitudinal section, sperm whale dentin has yellow “globules” included in the marbilization.

5. Hornbill Ivory
This comes from the casque or epithema of the Helmeted Hornbill, a bird native to the East Indies. It is distinguished from the rest of its family (the Bucerotidae) by having the front of its almost vertical and slightly convex epithema made of a solid mass of horn. This “horn” or “ivory” is quite hard and closely-textured. This substance is used to make small objects such as buckles and brooches, and is highly valued by the Chinese. In cross section, you can see a bright yellow interior with a scarlet rim.

6. Vegetable Ivory
The source of vegetable ivory is the inner seed of the South American ivory palm, and is thus completely made of cellulose (rather than collagen). These seeds are the size and shape of a small hen’s egg, are very hard, and are solid all the way through. Vegetable ivory is smooth, takes a good polish, easily absorbs dyes, and is relatively inexpensive. It is used for small items only, such as dice and buttons. Since about WWII, vegetable ivory has been largely replaced by plastics.

7. Synthetic Ivories
Since 1865, when it was first invented by Alexander Parkes, celluloid has been used as an excellent ivory substitute. Casein has also been used. Names for these “faux ivories” include French Ivory, Ivoride, Genuine French Ivory, Ivorine, etc. Both grain patterns and the engine turned effect are added — in general, the patterns of these are very regular in the fakes, and more irregular in the real thing. In instances of very good imitations (i.e. using celluloid), chemical tests are required to tell real ivory and the fakes apart.

Books Dealing with the Identification of Ivory

There are a few good books dealing with the identification of ivory. I currently have available *very* limited quantities (often single copies only) of the following out of print books (click on the dealer name for ordering information):

IVORY By Geoffrey Wills. Published by AS Barnes & Co. First American Edition. Hardcover, 95 pgs. Indexed. Synopsis: covers ivory identification, care, and uses around the world. Many black and white photographs and line drawings. Condition:Very good in Good dustjacket (some scuffing). UN601 $23.00  Available for order from Uniclectica Antiques and Collectibles.

Ivory: Pleasures and Treasures By O. Beigbeder. Published by G.P. Putnam, 1965. Synopsis: A nice overview of ivory carving through the ages — from the Prehistoric to the Baroque. *Many* detailed black and white and several great colour photographs of some spectacular ivories! Hardcover, 128pp. Condition: Good, with shelfwear. Dustjacket has a tear and penning on the front; boards have the same colour picture as the d/j – very nice! UN607 $19. Available for order from Uniclectica Antiques and Collectibles

The following are currently out of print, but are listed here for your information.

Is It Ivory? By Harvey Shell. Published by Ahio Publishing Co., 1983. Paperback.

Identification Guide for Ivory and Ivory Substitutes 2nd Edition. By E.O. Espinoza. Published by the World Wildlife Fund, 1992. Paperback.

Ivory By Geoffrey Wills. Published by AS Barnes and Co., 1969. Hardcover.


Cleaning and Repairing Ivory

Part of the Uniclectica Antiques and Collectibles Online Series “Caring For Your Antiques and Collectibles”

Always begin cleaning with the gentlest method, and gradually use more invasive techniques, as required. Due to ivory’s sensitivity to moisture, only dry cleaning methods should be used. If these are insufficient, consult a conservator with experience cleaning ivory.

You must always be careful that you are not trying to remove original surface coats, pigments or patinas! Also, because ivory so readily absorbs oils and stains, wear a pair of white cotton gloves with a good fit while working with ivory (these gloves are inexpensive, and are available from drug stores and photography shops).

Dry Cleaning Methods:
1. Soft Brush. Using a clean, soft paintbrush, brush the dirt off the object. Work slowly towards an edge.

2. Powdered Eraser. Grate white vinyl eraser, using a zester. It *must* be white vinyl eraser, as the pink erasers (or others) contain contaminants, such as colourants, sulphur, etc. Gently rub the grated eraser on the ivory, using either the soft brush or your fingertip (wear white cotton gloves, so that the ivory does not absorb the oils, etc. from your hands). Be certain to gently brush away all of the eraser flakes when you are done.

3. White Vinyl Eraser. Gently use a white vinyl eraser (ungrated) over the surface of the ivory. Be careful not to apply too much pressure, and to work on a small area at a time.

4. Groomstik. Groomstik is a natural rubber product, which is sticky. It pulls the dirt off of the surface of the ivory. It is available through museum supply houses — check with your local museum. Using a small piece of Groomstik, gently roll it across the surface of the ivory. Be careful not to pull off any small or loose pieces of ivory, or of pigment, etc.

If these cleaning methods do not work, again, contact a conservator experienced in working with ivory.