[Stoves] Crispin´s kiln. (was Re: Traditonal Charcola Making Process / retort

[Crispin Pemberton-Pigott]

Dear Jeff

If it was smooth and vitrified and air tight, that is a problem.  I would
prefer that the pores are first created and then the outside slightly
melted.  It has an orange peel look to it.  At a slightly lower temperature
it simply look porus.

I have some great pictures of cross sections of stoves (we had a smashing
good time) where the charcoal is not fully removed.  At the intersection of
the burned off / not burned off materials there is a foamed clay-charcoal
mix that I did not expect.  It has bigger bubbles than further in.

When you heat a clay pot too quickly, there are steam explosions and thin
sheets pop off the surface as the water inside boils.  With the stoves, a
similar effect is produced by the charcoal, but at a temperature so high
that the material is soft enough to inflate rather than shatter.  The cure
is patience.

>So it could be possible to have a porous substrate (clay) with a smooth
>outside surface.

Regards
Crispin