A couple of clips showing a comparison of proper softwood blacksmithing / bladesmithing charcoal with "overcooked" high temperature charcoal best suited for biochar applications.
Bladesmithing charcoal tests:
1. hard and clean, not crumbly and dusty
2. dense and solid, not spongy and blown out
3. musical and ringing when tapped, not dead and dull
4. burns with a blue and bright yellow flame, not a small dim orange flame
read more here: islandblacksmith.ca/2016/04/testing-bladesmithing-charcoal/
more about making blacksmithing charcoal: islandblacksmith.ca/how-charcoal-is-made