Working with Ivory and Bone
Fossil ivory comes from three sources—it is either walrus ivory that has been buried for hundreds to thousands of years or it is 10,000-plus-year-old ivory from the long extinct woolly mammoth or mastodon. All of these ivories have been buried for centuries and have absorbed minerals from the soil that have turned them varying colors from tan, orange, golden brown, and chocolate brown to even black; occasionally a blue or green color is also seen. This ivory is not truly fossilized in the sense that the ivory has been replaced with minerals/stone; it is really just beginning to become mineralized. It is in the earliest stages of fossilization and is just slightly harder than fresh ivory. "Fossil" ivory can be cut or worked with the same tools that regular ivory is worked with as listed below, the only difference you may notice is that due to the minerals it generally has a rather unpleasant smell when it is being sawn or sanded and it takes an even better shine than fresh ivory. Most "fossil" walrus ivory is found in the form of Eskimo artifacts, usually sled runners, large chopping tools (adzes or mauls) or net weights; this is because the Eskimo had lots of ivory and very little good wood. The Eskimo dig for these artifacts during the warm summer months at ancient village sites.
"Oosik" is an Eskimo word for the walrus penile bone. They range in size from 8" long to nearly 2 feet in length and several inches in diameter. Oosik is for the most part a very dense heavy bone and the large specimens were often used as clubs and sharpened as picks by the Eskimo. The front 2/3rds of the oosik is the densest, with just a porous center, and it can be used for slab handle knives or hidden tang handles. The bulbous back 1/3 is generally very porous and at best the outside can be sliced off to be used for thin knife handles. Fossil oosik has been buried for centuries and has obtained its color the same way the fossil ivory has; it also is not truly fossilized, only mineralized. When using as a knife handle material the porous core can either be ignored, covered with a butt cap, or filled with epoxy or a mixture of epoxy and glue, red or black powders or brown oosik dust. When the epoxy hardens, the excess can be sanded off along with the scaly oosik surface, and the sanded bone and epoxy will polish up glassy smooth. The Eskimo also dig these bones up during the short summer thaw. This exotic material is very beautiful and knife collectors have created a strong demand for it—they find its origins fascinating!
Working ivory is not unlike working hardwoods except that ivory and to a lesser degree oosik are both more sensitive to heat than woods, and this is the most important point to remember when working these materials. Nearly all cracks that result in worked ivory that has been properly cured are caused by overheating due to improper techniques when using machines for cutting, sanding and polishing the ivory or bone.
Ivory can be cut with any tool that will cut wood: a hack saw with coarse teeth, jewelers saw (for very fine work), or better yet if much cutting or any slabbing is to be done, a band saw. Metal cutting blades 1/2" wide with 6 to 10 teeth per inch seem to work the best. The fewer teeth per inch the less clogging with dust, but the more teeth per inch the smoother the cut and the less subsequent sanding required. With any saw, a sharp blade is essential as a dull blade will result in rough wandering cuts at best and scorched ivory at worst. The same goes for drill bits, burrs and sandpaper: the easier it cuts the cooler it cuts! If you cut a tusk into sections or chunks you should seal the pores on the cut ends to prevent rapid drying out and cracking. We have found smearing a white glue (such as Elmers) on the cut ends to be the most convenient method and we have never had a piece crack that was so protected. Hot wax or a varnish type finish can also be used but these are messy. To cut a tusk section into slabs many people glue the tusk section (with hot glue or epoxy) onto a board 1/2" to 1" thick, about the same length as your section and several inches wider. Line up the edge of the section to run parallel with one edge of the board when you glue it. The board will hold the ivory firmly in place as you run them both through the saw. The board offers a flat (non rocking) bottom and a square flat edge to run along the fence when slabbing, and the extra inches in width can be used for holding and pushing. Don't rush when you slab, ivory is extremely dense and pushing it through the saw too fast will result in wavy cuts—use light but steady and even pushing pressure. You can spray WD40 into the cut to cool and lubricate if necessary.
- When sanding ivory make sure you use fresh sandpaper or sanding belts that are good and "sharp."
- Dull sanding belts will overheat the ivory, and hand sanding with dull paper will burn you out! For band sawing and belt sanding ivory we recommend rigging up a vacuum cleaner to cut down on the dust.
- Ivory dust is not toxic, but wearing a dust mask makes sense. Wet sanding with wet and dry (silicon carbide) sanding paper is our choice for sanding ivory, as there is no dust and no heat.
- Wet sanding mammoth ivory or fossil walrus ivory is not recommended if the ivory has lost some of its integrity and is getting chalky.
- A smooth surface will not be easily attained. To wet sand use a bucket of water or the sink and wet the paper and/or the ivory enough to keep the ivory dust/paste washed off the paper and the ivory piece— the paper never gets clogged, there is no dust, the paper lasts much longer and there is no heat.
- Whether you dry sand or wet sand you should start out with a coarse grit paper to remove the saw marks, either a 120 or 180, and when you have all saw marks out you will go to 240 grit to remove all of the coarse scratches.
- When this is complete you go to 400 and then final sanding with 600 grit paper and this will give you an almost matte finish.
- Don't rush from one grade of paper to the next before you have the scratches removed from the previous grit—you will either end up going back to the previous grit to remove earlier deep scratches or you will spend more time trying to get them out with the fine grit paper.
- Getting a mirror smooth finish by hand can take practice; try rubbing with Simichrome metal polish or auto polishing compound on a rag. The best results come from a fast spinning buffing or polishing wheel. We prefer an unsewn 54 ply 6" muslin wheel with a small reinforced hole for use on a tapered spindle.
- The polishing compounds come in a waxy block or stick form and are impregnated with fine abrasives. By holding the bar against the spinning wheel you will "charge up" the wheel with abrasive.
- Use tripoli or bobbing compound first to remove any fine sanding scratches and to get a nice shine.
- Don't hold the piece in one spot or press it hard into the wheel; this will nearly guarantee the development of the tiny cracks referred to as crazing (it may take weeks or even months for them to show up). Then with a different buffing wheel use chromium oxide, Zam, Fabuluster, or white rouge to put the glassy sheen on the ivory.
- Red rouge works but is messy and gets hot. Overheating cooks the beauty right out of fresh ivory, oosik and "fossil" ivory and will result in a milky cast. This telltale symptom of overheating is a sure sign that crazing will follow.
- If you overheat the oosik or ivory and it turns milky we recommend sanding off the milky surface and starting over. If you are polishing ivory that has metal adjoining it such as an ivory handled knife with a metal bolster or metal pins in the handle, be careful that you don't heat up the metal. It heats up faster than ivory and holds the heat and transfers it to the ivory.
- Take your time finishing the ivory and metal, keep it moving and keep it cool. If it’s too hot to comfortably hold, it’s too hot. If you are making an ivory handled knife with pins in the handle, drill the pin holes in the ivory just a bit oversized and fill the gap with glue, ivory expands and contracts, tight pins can cause cracking.
- Be cautious when peening pins on ivory handles. If you want to clean the waxy polishing compound off ivory handles or out of carvings, try lighter fluid on a toothbrush or a cloth, Ronsonol work fine.
- You can make a satisfactory buffing machine using an old washing machine motor. Mount a tapered spindle on the shaft so you can quick change between your coarse and your final buffing wheels. Compounds, buffing wheels and spindles can be purchased at hardware stores, lapidary shops or through knife making suppliers.
Some knife makers and scrimshanders use mineral oil to protect the ivory from shrinking or cracking due to dry climate or lack of humidity; this seems to work best with slabs and thin pieces.
- Place the unpolished slabs in mineral oil for several days, then remove, wipe off and store in a plastic bag until you're ready to use it; the ivory will absorb some oil and after being sanded and polished will allow even less moisture to escape thereby reducing the possibility of shrinking and cracking.
- Another technique for oiling ivory is to put the ivory in a double boiler pan (water in bottom pan) with enough mineral oil to cover the ivory slices and gradually increase the temperature of the ivory to the point where the ivory sends up tiny bubbles of air/moisture. Leave the pan on the stove for about eight hours, and raise the temperature if the bubbling stops, but the oil should not be boiling.
- After the eight hours turn off the heat and allow to cool, wipe off the oil and store until you are ready to use; the moisture in the ivory has been replaced with oil, you will not be able to see a difference. We do not recommend these oil soaking treatments for fossil ivory, as it can get an oil soaked look. Your natural skin oil rubbed on ivory will help turn the ivory yellow faster and give it that antique look.
When storing ivory in any form, raw, sliced or finished, the best policy is to keep it in an area that has a high humidity. A basement is better than an attic, a cabinet with a cup of water is better than an open book shelf. Common sense care of your ivory will help it grow more beautiful as the years go by.