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Exotic Materials in the Decorative Arts:
Keys to the Identification of Ivory
By Lisa G. Erickson and Terry S. Gross, Urban Chateau

INTRODUCTION
Some of the most beautiful objects of art throughout history have been created with one or a combination of exotic natural materials. From precious gems and metals to shagreen, tortoiseshell and ivory, natural materials have earned an esteemed place in the Decorative Arts. The more rare and exotic the material, the more desired and expensive, leading to a great demand for imitations. The ability to distinguish between the actual valuable material and the imitation is of utmost importance to the collector when evaluating antique furniture and objects of art for purchase. Each exotic material has its own unique characteristics and therefore imitations, meriting full and individual attention. This article will focus on identifying authentic ivory through observational techniques as an introduction to this nuanced study.

As antiquaires we have had many experiences when buying antique pieces crafted from natural materials. One relevant experience to recall was our attraction to a beautiful "ivory" inlaid center table near the back of a poorly lit European antique shop. The owner believed the inlay to be ivory which would justify the price of the table. We moved the table into the light and after investigating became certain that the inlay in fact was not ivory. We did not purchase the table. In another example, we found an early 20th Century piece with a raised stem the owner had mistakenly labeled as Bakelite. Upon close inspection we were certain that the stem was ivory and therefore a more important piece, so we completed the purchase. In this article we would like to share what we look for and why.

HISTORY
For thousands of years ivory has been esteemed for both practical and aesthetic reasons. Harder and more durable than wood or bone, ivory doesn't chip, crack or break easily with use, and deteriorates very little over time. This chacteristic made it an ideal material for early man, who used it to craft tools and weaponry, especially before the discovery of metalworking. Ivory has traveled along various trade routes in caravans with other precious materials like spices and silk throughout history, literally becoming more expensive (and thus more luxurious) with every mile. Generally speaking, the more exotic something is the more desire it instills; even in biblical times the King commanded that "every three years the ships of Tarshish would arrive bearing gold, silver, ivory, apes and peacocks." (Chronicles 9:21)

Strictly speaking, ivory is any tooth with commercial value and can come from a variety of mammals, such as hippo, warthog, walrus, sperm whale and narwhale. This article will focus on elephant ivory because it is the most important and preferred in Western culture, due to the large scale, creamy color, close-grained texture and pleasing smoothness that makes elephant ivory a superior substance for the Decorative Arts.

Always precious due to relative scarcity and thus a symbol of wealth, elephant ivory excels as a material for carving, turning, veneering and painting upon. Much ivory work survives from ancient Egyptian, Greek and Roman art, especially in sculpture, bas-relief, and inlay. Ivory objects epitomized valor and prestige before the advent of modern weaponry, when hunting elephants was very dangerous. From Early Christian times through the Middle Ages, ivory was considered the most noble substance for personal and devotional objects, perhaps because Christ's body was depicted as "...the work of a sculptor, hard and smooth as ivory" (Solomon 5:14), instilling the material with biblical virtues of purity and chastity. During the Renaissance, ivory turning was considered an integral part of a young prince's education, due to the patience, steady hand and precision required to work the delicate and noble material on the lathe.

New sources for ivory emerged with colonial exploration in the 16th Century, rising again throughout the 18th and 19th centuries as European power spread throughout Africa. However, it was the Industrial Revolution – the new ability for mass production, increased ease and range of travel, more efficient ways to transport raw materials, and an insatiable appetite of the new middle class for luxury items formerly limited to the extremely rich – that lead to the wholesale slaughter for tusks that endangers elephants as a population today. The resulting lack of supply and subsequent higher costs increased the use of natural substitutes and fueled the development of man-made simulations in the 19th Century.

These ivory imitators can be quite convincing to the untrained or naked eye. Some fake ivory objects are old enough to be antiques in their own right, complete with patina and authentic stylistic character. This article will arm you with clues and observational techniques you can use to identify ivory with your eye or jeweler's loop on site before purchasing.

MORPHOLOGY

The first step to spotting fakes is to understand the origin and morphology of natural elephant ivory. The tusks of Asian or African elephants, which can grow to just over 11 feet, with an oval cross section of 8-10 inches, are massive upper incisors, similar in structure to human teeth, with nourishing blood vessels occurring only in the root. The majority of the tooth is solid, composed of the dense mineral substance dentine. 70% inorganic and 30% collagen in composition, Dentine is deposited layer upon layer as the tusk grows, creating a very characteristic internal "growth pattern", similar to the growth rings of a tree.

When true elephant ivory is carved or cut these growth patterns are exposed, appearing as intersecting lines or crosshatching. The resulting intersecting patterns are called Schreger lines, clearly visible on the solid ivory sphere (Figure 1a-b). These patterns are the most important characteristic when identifying elephant ivory. Though more difficult to find on objects of art, careful scrutiny of surfaces and different angles, such as underneath the carving, should reveal Schreger lines if the piece is truly elephant ivory. Examples of the way these lines appear on two separate antique objects are demonstrated in Figure 2a.

Schreger lines appear on the very top of a 19th Century ivory sculpture of a Roman General (Figure 2a) whereas they are found on the underside in the case of a 19th Century horse crop carving (Figure 2b).

There are other important keys to identification characteristics: the surface is smooth, and semi-translucent; ivory is solid, very dense and cool to the touch (due to the high mineral content); the natural overall curve of the tusk is often visible in larger objects. Ivory tends to yellow and split in the direction of the growth pattern over time, much like wood, the cracks often blackening with age. An example of this third tendency is shown in Figure 1b, demonstrating the cracking and blackening on a solid ivory sphere.

These other keys to identifying ivory are especially important when trying to identify flat surfaces such as ivory veneers or inlays where Schreger lines are not always as visible. True ivory veneers from two separate antique pieces, a box and a table, are illustrated in Figure 3a.

Upon first glance, the cracks exhibited on the 19th Century decorative box (Figure 3a), might appear as normal cracks caused by stress inserting the roundels. However the fact that the cracks occur in various directions indicates that the surface has split differently along the growth lines depending on how the veneers were sliced.

The cracking is also visible in the 19th Century ivory inlaid center table from the early 19th Century (Figure 3b). Any Schreger lines are masked by the fine etched and ink rubbed surface. Another indication of ivory inlay is the quality of the etched artwork and general craftsmanship. The large-scale slab center veneer is also indicative of elephant ivory. The conclusion that these veneers are authentic ivory is further confirmed when we understand the characteristics of the most common natural imitation – bone.

IMITATION OR FAKE IVORY: BONE

The most predominant naturally occurring ivory imitator is polished bone. Used for thousands of years as an inexpensive alternative to ivory, bone is quite easy to detect if one knows what to look for. Again, it is important to understand the basic morphology of the material. The center of bone is a spongy marrow cavity and the ends are unusable, limiting the size of viable material for carving (Figure 4a). Elephant bones are the largest suitable for Decorative Arts but are at most about a half inch thick when hollowed and trimmed of unusable material, making bone a poor substitute for large carvings and solid objects. More opaque and much whiter than ivory unless dyed yellow, bone doesn't tend to split with age. Carved bone cannot achieve the same amount of fine detail of ivory because it lacks a fine tight grain.

Unlike ivory, bone is a living tissue, highly nourished by blood vessels that leave telltale channels in the surface, sometimes visible to the naked eye. Depending on how the bone is sliced, these tiny irregularities will

appear as dark spots, pits, dashes, or lines (Figure 4b). Bone is often bleached and polished to mask the appearance of these blood vessel channels, but they are always present and dirt tends to collect in these imperfections, darkening with age. If these organic markings are present under a 10x loop, you can almost surely rule out ivory, as we did when examining the inlaid table in our introduction. The telltale black spots were clearly visible in the sunlight using our jeweler's loop. We knew our "ivory" was truly bone.

IMITATION OR FAKE IVORY: SYNTHETIC PLASTICS
In the mid 19th Century synthetic

plastics were invented and were quickly used to emulate precious substances, including ivory. There are several types of plastic imitators with their own set of characteristics. Celluloid, invented in 1869, can be identified by the regularity of the pattern that attempts to emulate the Schreger lines, clearly visible under magnification (Figure 6b). The pattern found in Celluloid is created by two similar tones of cream-colored plastic, often appearing as banded lines or swirls, but lacking the subtly of true Schreger lines. Celluloid is also more brittle and less dense than ivory and often smells of camphor when rubbed vigorously. Casein plastic, made from milk, is too lightweight to be ivory, has no surface texture, and is waxy to the touch.

In general, the surfaces of modern plastics and resins are featureless, showing no grain. Synthetic plastics are molded, leaving evidence such as seams, rounded raised portions, jagged edge pits and broken bubbles visible under the loop. An important key to identifying plastics is the inevitable result of the molding process, often leaving rough or obvious tool marks such as turning marks. Visible under a jeweler's loop (Figure 5a-b), these are sometimes diminished during the finishing process. Another important key is that synthetic plastics will be warm when placed on your cheek and continue to warm while ivory stays cool longer due to high mineral content. Also, modern plastics rarely demonstrate the kind of craftsmanship merited for luxury ivory goods.

Access to a black light and total darkness is a scientific way to rule out the myriad of synthetic plastics. Ivory will reflect the full spectrum, appearing bright blue (bone will appear identical due to similarly high mineral content, so beware!). Plastics absorb part of the spectrum, appearing from a dull-blue color to an off-color like mauve, depending on composition. Usually we do not have this opportunity when out buying antiques, so rely on the observational techniques described in this article.

SUMMARY
When evaluating ivory antiques we suggest methodically asking yourself a series of questions to deliberate whether an object is truly ivory or not. Weighing the outcome of your observations will yield a credible probability even when the results are not initially definitive or clear-cut. A process of elimination is often essential, especially when examining inlays and veneers. Close-up photos (Figure 6) of genuine ivory (6a), bone (6b), celluloid (6c), and modern resin(6d) are juxtaposed for comparison to illustrate what surface characteristics to look for when identifying ivory.

When examining an antique, we suggest taking these basic steps: Check for signs of ivory: Turn the object slowly in the light using a 10x loop and look closely for Schreger lines. Can you find any signs of growth patterns, grain or crosshatching? Is there any splitting, dark cracks or subtle yellowing on the surface? Is the overall quality of the piece fine enough to merit ivory?

Check for signs of bone: Bring the piece into the light, looking for irregularities on the surface. Are there spots, dashes or lines visible? Is the color too white or overly yellow (indicating dye)? Do the pieces exceed the size possible for bone? Does the quality of craftsmanship hint that an inferior material might have been used?

Check for signs of plastic: Does the surface appear featureless, showing no grain or have an unnatural pattern? Do the veneers look organic or molded? Are there any signs of manufacture such as mold lines, bubbles or jagged pits in the surface? Does it have a waxy texture, smell odd when rubbed or feel warm to the touch?

As an educated buyer, armed with these keys to identifying ivory, you can focus on enjoying the beautiful creamy quality of this exceptional material that had such a deep impact on the Decorative Arts and History itself.