Q: What is fossil ivory? Is it petrified? Can you carve it?
A: Fossil ivory is found all over the world, but the only kind considered useful for carving is found in regions of the far north where the ground is frozen for all but short periods of the year. Instead of decaying or undergoing petrification, ivory from animals that died hundreds or even thousands of years ago often remains much as it was, sometimes taking on coloration from surrounding minerals. This can often result in startling colors and patterns, which may be brought out by skillful carving and polishing. Shades of brown are most common, but some mastodon ivory, for example, exhibits a startling blue venation.
The kinds most commonly found are walrus and extinct Proboscidea—usually mammoth or mastodon. Fossil walrus ivory, both the long tusks and the short back teeth, weathers out of stream beds during spring thaws, and is collected by native people to supplement their incomes. The Proboscidean ivory is generally found in mining operations, or in deposits near ancient lake beds in Siberia, where it has been a resource for centuries.
Fossil mammoth ivory can come in the form of whole perfect tusks—these are often mounted as specimens. The tusks can also delaminate into long curved sheets of fairly thin material arranged concentrically around the core. While not suitable for carving anything large in the round, this “bark” can be useful for long thin items. Proboscidean ivory may be recognized by the grain pattern visible in a cross-section, which displays a double spiral pattern, a series of clockwise spirals crossing others running counter-clockwise. If one thinks of the crossings of these spirals as being the points of a star shape, ivory with acute angles at the points of the star is from modern elephants, mammoth and mastodon ivory shows obtuse angles instead. Workable material will have a certain sheen and translucence—if it appears chalky and dull it is probably too deteriorated to be of much use.
Walrus tusks were often modified slightly for use as ice axes, by flattening a section to facilitate the attachment of a handle, then they were lost or discarded. These artifacts, if not archeologically significant, are often used as raw material. Ancient walrus ivory does not differ much from modern except in coloration. There is a hard enamel layer on the outside of the tusk, usually no more than ½ cm. thick, then there is a layer of dentin, best for carving, which does not display much if any grain. The core of the tusk is distinctly different, having a characteristic grain pattern resembling tightly compressed spheroids. This is slightly softer than the dentin layer, but is still carvable. The back teeth range from about 3 cm. to 7 cm. in length, and rarely exceed 3 cm. in thickness. Their structure is different from the tusks. The enamel layer is not as thick or as distinct from the dentin, and the core in cross-section displays a pattern of rays superimposed over a concentric banding. One may often observe a chatoyant effect in crosscuts of this core material, especially in the teeth that seem most deteriorated on the outside. The dentin layer may have separated from the core while it has been aging—sometimes this may be ascertained by looking carefully at the worn surface of the tooth. This ivory may be carved in much the same way as dense wood might be, although wood has more grain-preference.
Ivory can be polished on the end-grain as successfully as on the long grain, and it lacks the array of pores characteristic of wood or bone. It works very much like bone, and I advise beginners to work on some bone first—having beef shanks for dinner (slowly cook three hours in a frying pan with a wine-tomato sauce—yum! ) will provide enough material for hours of carving. Saws can be useful in preparing the material, then I prefer to use sharp carbide burs for the roughing-out, working with gravers, scrapers, and/or files to refine the surface. Decreasing grits of abrasive paper may also be used; by hand or as flap-wheels. Fossil ivory will take a high to medium polish, depending on the density of the material. In all cutting and polishing operations it is imperative to minimize the generation of heat, which will quickly destroy the surface, turning it whitish and crumbly. One should use light strokes, well spaced, avoid bearing down in one spot, and always keep moving, both in carving and polishing. For a final polish, white rouge may be used, or various proprietary polishing compounds meant for plastic. Avoid polishing compounds that are strongly colored, as they can stain the material.