How is wood charcoal made locally? What other substances are formed in the process?

Locally, wood charcoal is prepared by the following steps:

1. Logs of wood are piled one above the other with a gap in the centre of the pile.
2. The pile is covered with wet clay to prevent the entry of air.
3. A few holes are left at the bottom of the pile.
4. The wood is set on fire.
5. When the fire dies out a greyish-black, brittle, porous solid is left behind which is wood charcoal.

The other substances formed are wood tar, wood gas, pyroligneous acid.