That's interesting. Very common here. Mostly with Elm. I never get it with softwoods. Actually barely even get any ash when I burn pine.My Jotul F600 CB must be burning that carbon. Ash in the Jotul drops through a grate in the base in the stove into an ash pan that has a separate door. The gaps in the grate are about 1/4 inch or so. Not a clinker in 20 years.
Yes. More than likely this is it.Maybe the clinkers are silica.
Trees do pull silica from the soil into their tissue.
Carbon gets lots of love from ecologists. Removing snow from a section of forest, however, shows that silica warrants attention, too.www.futurity.org