Guys,
I use a mix of 1/3 hardwood charcoal, 1/3 leather charcoal, 1/3 bone charcoal. This is an age old case hardening formula that I got from somewhere ( I forget where ). I make the charcoal the same way as making charred cloth, a metal container with a few small holes. Fill the container with the material and stick it in the coals of a fire. When the smoke stops coming out of the holes, remove the container from the coals and let it cool. Bone charcoal - I bought a box of bone meal at a garden shop. To case harden I put the small parts in a sealed metal container that is filled with the charcoal. I use a small lead melting pot with a flat steel plate for the lid. Put the container in the fire and heat it red hot, for a long time, like when I have a nice fire in the fireplace on a cold evening - several hours. Then remove the container from the fire and let it cool. Take the parts out and reheat them to cherry red and quench in brine.
At one time I tried to dump the red hot mix of parts and charcoal directly into the brine - a big mistake. Bad scalds on my forearms - ouch! Also, don't try to caseharden parts made from 12L14 steel, often used for screws, it doesn't work well.
Jim