2 wood charcoal to one bone charcoal, but I'm getting much better colors with a reused mixture. Make sure it's held at 1375 for 1 1/2 hours and then when quenched, needs to be as close to that tempo as possible and hold your crucible nearly in the water when you dump it to keep that temp. If it cools much, you'll get a lot of grey colour and that's not really what you want. You can call me to pick my brain, and I'm about to write an article for the journal on all of this. I'll be glad to help you anyway I can. Jerry