the complete text of an article I authored about saggar-firing,
entitled "Fast Fossils: Carbon-Film Transfer on Saggar-Fired
Porcelain," originally published in Ceramics Monthly
Magazine, (USA), March 2000 issue.
"Saggar" is a term used for any structure which encloses a pot during
firing: it could refer to a large lidded pot which encloses a smaller
pot. Even an enclosure of stacked bricks with a kiln-shelf "lid" would
qualify as a "saggar".
In earlier times when kilns were fired with "dirty-burning" wood or
coal, saggars were used to protect the pots from the undesirable residue
of the combustion process. With the advent of cleaner-burning fuels,
the necessity for saggars diminished.
More recently potters have again begun to use saggars - but in a way
exactly opposite their original intent: instead of using saggars to
protect pots from an outside atmosphere, potters now utilize saggars
to encapsulate pots within a very specialized atmosphere.
My approach to saggar firing is to wrap pots in fresh vegetation and
place them in the saggar on their sides, atop a bed of sawdust. I then
cover the pot entirely with sawdust and place the lid on the saggar.
During the firing, due to the presence of heat and pressure - and due
to the relative absence of oxygen the vegetation turns to "activated
charcoal", and in the process, releases a film of carbon.
When everything works just right, the film of carbon penetrates the
porous porcelain pot. The images you see on the pots are the result
of that "carbon transfer". (Paleontologists have told me that this process
is very similar to the fossil-formation process called "Carbonization"..or
"Carbon Film Transfer".)
This approach to saggar firing is capricious and rather uncontrollable,
and the losses high. As in the production of fossils in nature, all
the ubiquitous variables must precisely coincide to create these marvelous
saggar fired images. Yet I find that the best results make the pursuit
worth the losses.