The process described by Damascus is essentially identical to one found in an old Machinery's Handbook I have with a 1946 copyright date. They recommend putting the part in the charcoal, in an iron pot & then stirring while bringing up to heat. They also mention that sand or wood ashes can be used for a lighter color, but for the darker color pulverized charcoal should be used. No mention is made of sealing the container or that the charcoal should be bone derived, seems to indicate ordinary wood charcoal.
The American Gas Furnace process is also mentioned in this book & it does specify charred bone to be used. Also a liquid is injected during the tumbling process. What this liquid is, is not specified, probably because it was a patented process.
