Note: the following is a long discussion of and instruction for bone
cleaning and preparation, not exactly graphic, but nonetheless specific.

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 the 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
acrid 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.

Sean Barry

*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.