Charcoal (Knowledge)

A New Combustible
''Sometimes when burning wood, after a large fire, some pieces of wood burn but didn't turn into ashes. They look grey and porous, and after trying to light a new fire with them they appear to burn even hotter than normal wood while producing little smoke and are easier to light. If we could figure out exactly how to make these out of wood, we could use them in our pottery kilns and other industries instead of wood, increasing their efficiency!''

Potential Requirements
Dancing naked outside of your house, with piece of charcoal stripped to your forehead might trigger it.

If not then ???

Consistently supply less wood than desired by your industry. roughly 50% should do it.