for Musical Instruments
The following is an excellent description of how to clean bone thoroughly, written by Sean Barry, luthier and formerly museum curator.
It's easy but involved to prepare bone really really properly for instrument work--I found that my experience as a vertebrate museum curator/preparator at UC was invaluable in this regard because it taught me how to prepare bone really well, and how short-lived some crafts processes really are (museum material is prepared so that it will survive for centuries). The main problem in lutherie is producing material that will do the job, last a long time, and not damage the instrument it was meant to enhance. That means that lutherie bone must be very clean and grease-free and therefore stable and harmless to nearby materials. Cleaning and degreasing are conceptually and technically easy, but natural materials being what they are, it's sometimes too easy to lose patience with the preparative process and accept "almost-right" material. Don't.
Source material is pretty easy--the best place to look is a grocery store. Buy a fresh cow "knuckle" or a section of long bone, (commonly sold for soup, often not on display but almost always available). You can also use other species and bones, but cow bone has the virtues of density, size, and limited (sometimes nonexistent) marrow cavity. Ask the butcher to saw the knobby ends from the bone, or do it yourself with a bandsaw or hacksaw. Extract as much soft tissue as possible from the exposed marrow cavity (straightened wire coat hanger and compressed air is a wonderful combination), then immerse the bone in water or water with household ammonia or a little mild detergent added. The ammonia method cleans best and fastest but requires a stove with an efficient exhaust hood, the detergent is not too far behind (Ivory liquid or similar), and pure water works well but takes longer. The advantage of pure water is that the resulting broth is soup. Bring the liquid to a boil, then reduce heat and simmer for 30-40 minutes (ammonia in water), 50-90 minutes (detergent in water), or up to two hours (pure water). The object is to cook away the soft tissue and begin the degreasing process. After the assigned time, remove and cool the bone, then use running water in combination with fingernails and a stiff brush to remove the remaining soft tissue--don't be afraid to return to the simmer pot.
After the bone is cleaned of soft tissue, air-dry for a day or so, then cut with a bandsaw or hacksaw to oversize blanks (bridge, nut, saddles, etc). Air-dry the blanks for at least 2-3 days, perhaps a week during humid times--to degrease properly they really have to be bone-dry, so to speak..... Degreasing is the most overlooked and under-done step in bone preparation, even in a few museum preps. Greasy bone will leach fat slowly but forever, and the grease will contaminate glue joints, make finish and wood part company, stain and degrade wood, and itself eventually destroy the bone through a process of slow combustion (one carbon at a time). I once attempted to repair a Martin D28 with a homemade bone saddle that had leached grease right through the ebony, so that it had seeped into the top, caused the bridge AND BRIDGE PLATE to loosen, and was almost impossible to remove completely so that a new bridge and bridge plate could be installed. I still have nightmares.... Trouble is, bone can look clean yet have a substantial grease content that won't manifest itself for years, but by then some of the damage will be much too advanced to fix. If I've made you paranoid about bone grease and convinced you to avoid using bone that even has the hint of a tiny possibility that there might be a microliter of grease somewhere in it, good.
To degrease bone, immerse the very dry blanks in about ten volumes of white gas for 1-3 _weeks_. White gas, AKA Coleman fuel, is really flammable and so this step should be done in a glass container outdoors somewhere in the shade far from structures. Really greasy bone will discolor the white gas after just a day or two so replace it at that time. The safest disposal for small amounts of white gas is probably to allow it to dissipate into the atmosphere, but if you decide to go into production and generate lots of waste white gas, best make prior arrangements for its legal disposal. BTW, museum preparators use much more toxic solvents, such as carbon tetrachloride (CCl4), but only under extremely carefully controlled conditions that are simply not available out in the real world. Improperly vented CCl4 will eat your liver and cause you to die very prematurely, to put it bluntly, so that's why I recommend white gas (which is bad enough).
After the requisite degrease time (which can and should be extended if the bone shows any sign of residual grease, such as translucent spots), remove the bone blanks from the gasoline, rinse once in clean gas, and air-dry. Degreased bone should dry really fast, like in much less than an hour--if it doesn't, there is residual grease in the bone so put it back in a new gasoline bath. Again, I can't over-emphasize the importance of thorough degreasing--you could badly damage someone's valuable instrument if you use greasy bone.
Next, shape and final-fit (but don't install yet) the bone item--nut, saddle, etc, and polish it with fine compound (tripoli, then rouge, after smoothing with a file and wet-or-dry sandpaper. If the bone is not white enough (an individual preference--it will be pretty white after degreasing, but not glistening white), bleach with hydrogen peroxide. I use 3% peroxide, the garden variety drugstore purported antiseptic, and immerse the bone for about ten minutes. Longer tends to overwhiten and make the bone look flat. Air-dry and glue in place. DO NOT USE HOUSEHOLD BLEACH FOR THIS OPERATION!!. It won't bleach, and it seeps into bone and comes back later to haunt you--it makes the bone friable, but usually not for several years. Museum people generally avoid bleach, because though in years past it was sometimes used for skeletal preparations, most such specimens have long since literally crumbled to dust. Nowadays museum people almost universally use ammonia (at household strength) for chemical cleaning of skeletal material. Bleach is potentially useful during the cleaning process, but ammonia is so much safer for the bone and just as effective for cleaning that the choice is clear. Ammonia also begins the degreasing process (as does detergent), which bleach won't. Also,never mix household bleach and household or any other kind of primary ammonia (NH4OH.H2O), because your final memory will be of the pretty green but lethal chlorine gas that emanates and causes pulmonary edema.
I realize this was much more than most want to know about where bone comes from, but like any preparative process for natural materials (wood seasoning, etc), the bone-cleaning process is involved* and best done properly start to finish if you want your nut/saddle/bridge to look nice, work well, and last longest.
*Also, if the above seems very involved and tedious, it's because it is, and that's why for most of my work I purchase bone and saddle blanks from the various lutherie suppliers. These are imported from Japan, and are marvelously clean, grease-free, and inexpensive. The above instruction is really necessary only for unusually large bone pieces, which this post addressed.
**I've heard several times that cow bone available in pet stores for dogs is grease-free, though I don't know how they would do that without making it potentially toxic. Perhaps some is, but all of the pet store bones I've examined the past few years have contained some grease, just not evident until one warms the bone in the sun for a few hours. Again, your pet store bone mileage may vary, but to me the stakes are much too high to risk using it.