Introduction: Prepare Bone for Carving
A previous 'Ible called for a piece of "cleaned bone" in the list of things needed.
I later had a look at the site and could not find an 'Ible explaining how to get from dead animal to carvable substance, hence this one.
The principal aim of preparing bone is to remove all of the fat, tendon, muscle and other tissue which can leach into the bone, and leave a single piece of bone from which work-pieces can be selected. It really needs to be done on an uncooked bone.
When selecting a bone from the butchers, the best piece is a beef cannon bone. They are load-bearing which means that the bone structure is very dense, and they are one of the large bones which means that it is possible to get a decent sized piece of usable cleaned bone.
Some butchers will cut the bone in half lengthwise if asked. This will make the process of cleaning easier, but does limit your ability to select where the cut will be made.
While preparing the bone is pretty safe, you will be using a saw, a sharp knife and bleach, so use appropriate care.
A bone from the butchers
A small, sharp knife
A round rasp
Optional:- If you have a bottle-brush, that is useful, but a paper towel can be used.
Step 1: Removing the Epiphyses
It's amazing what exciting words you can learn from Wikipedia. I would have called these the "knobbly bits" but they actually have a real name.
To remove the knobbly bits, place the bone on a suitably firm surface. It might be necessary to try a few orientations until you find one where the bone feels stable.
Tension the hacksaw blade up good and tight, pick a point where the knobbly bit transitions to the straight bit and go for it. A fine-tooth hacksaw will go through the bone pretty easily, so there's no need to hurry. As long as you are making sawdust, you are cutting.
Once one knobbly bit is off, attack the other end. Again, it is worth trying various orientations of the bone on the cutting surface to find one where it is stable.
After you've got the ends off, you can dismantle the hacksaw and give it a wash in hot water with washing-up liquid. If your saw is entirely metal, then it should be OK in the dishwasher (no guarantees though). Remember to dry it thoroughly as soon as it is clean.
If your saw and blade were clean before you started, then you can use the knobbly bits for stock. Otherwise a passing dog will enjoy them.
Step 2: Removing the Periosteum. and the Marrow
Another new word, the periosteum is the fibrous membrane covering the bone. Like all non-bone components, it must be removed.
Stand the bone on its end on a chopping board and scrape the a small knife with a non-serrated blade down the surface. This should remove the last vestiges of meat from the bone, and with a little care you will get the membrane as well. You do not need to get everything, as we will be coming back to this task again later.
Once the outside of the bone is clean-ish, remove the bone marrow. This is fairly soft and squidgy, and can be dug out with the point of a knife. Once you've got a decent size hole right the way through the bone, you're done with this step.
If you're making stock, the marrow and other scraps can go in as well, and you will get a huge amount of beef fat out of the other end.
Step 3: First Wash
Take a bucket which is big enough to hold the bone and half-fill it with hot water from the tap. You don't want boiling water as that will encourage the fat left in the marrow to stain the bone, so hot, not boiling!
Add one scoop of soap powder (or whatever you would give to a load of laundry in your local water) and one cup of bleach.
Lay the bone in the mixture, making sure that the void in the middle is filled (i.e. lower it gently in).
Now leave it in a quiet place for twenty-four hours. I would recommend a garage/shed as the mixture of bleach and raw meat which emanates from the bucket is not the nicest. I would recommend against leaving it outside where an animal could engage with it.
Step 4: Second Scrape
Once the bone has soaked for a day, drain the liquid and rinse the bone in cold water.
The periosteum will be much softer after its relaxing bath and so you should be able to get all of it off the bone at this point.
There is an artery which supplies blood to the inside of the bone and this has to be found and removed. That is shown in photographs 4, 5 and 6 above. The blood vessel can be teased out of its hole with a knife point and a bit of care. It is important to get all of the artery as it will stain the bone if left in. If it breaks when you are removing it, then try probing the hole with a flexible piece of wire to clear it.
This is now the time to have another go at anything still stuck to the outside of the bone. Since the bone has been in bleach for a day, you should throw the scrapings away rather than making soup or a happy dog.
Step 5: Remove the Trabecula
The trabecula (not to be confused with Tribeca, nor with Benbecula) is the spongy bone towards the end of the inside of the piece. It is called "spongy" because it is full of holes: it is actually quite crunchy.
It holds a lot of fat which would stain the final piece, so it needs to come out.
Attacking from each end, chop down with a solid knife into the trabecula going as far as you can. You will probably need to sharpen your knife after this exercise.
Once you've got as much of the crunchy sponge out as you can, clean the inside of the bone with a bottle-brush or else just jam a few paper towels through it.
Step 6: Second Wash
As they say in the shampoo commercials:- rinse and repeat. See "First Wash" for detailed instructions.
Again, leave the bone soaking for a day.
Step 7: Removing the Metaphysis
The part of the bone where the spongy bone ends and the solid bone begins is called the metaphysis (TIL).
It is important that the bone is left to dry thoroughly before this step, so that the different components of it show clearly.
Once dry, it should be possible to see exactly where the spongy bone ends. It is always hard to throw away material at this point, but you have to be strong. Any spongy bone left will mar whatever you are making, so cut away the pieces of bone where it looks as if more than a tiny amount of the wall thickness is spongy.
Once you've thrown that bit away, get into the ends of the bone and get rid of the last of the spongy bone. I show a file and a rotary rasp bit doing the job. Keep at it until there is nothing which is not bone-coloured in view. Even a tiny patch of darker material needs to be abraded away, and that needs to happen inside and out.
Step 8: Ready to Carve
Now the bone is nothing but endosteum, it's time to decide what you want to make. Since bone is a natural material every one is different. It may even be that you can rely on a quirk of the initial shape to inspire whatever you create.
You can try different shapes and orientations by drawing on the bone with a B or BB pencil. That won't stain, and can be easily removed by a pencil eraser when you want to change it.
Good luck and good carving :-)