Jim Behan on wed 8 dec 99
I was recently involved in the firing of a large wood fired salt kiln. The
pots were made from a wide range of clays with varying proportions of
Iron. Some of the pots were also slipped with high alumina slips. The kiln
was fired over 16 hrs. to cone 10, crash cooled to 1000deg.C and clammed
up. All the pots emerged a pale /concrete grey to beige, many of them with
good salting and fly ash effects but with very little of the iron tones one
expected. A selection of these pots was refired over 6hrs in a small
fibre-lined gas kiln under moderate reduction to Cone 10. All were
transformed with the beautiful glowing oranges and tans that one looked for
in the first firing. A mug that was dry grey with no apparent salting came
out a rich silky brown reminiscent of the classic Dwight or Doulton
saltglaze surface.
Has anyone been here before and can anyone explain this phenomenon?
Hank Murrow on thu 9 dec 99
>----------------------------Original message----------------------------
>I was recently involved in the firing of a large wood fired salt kiln. The
>pots were made from a wide range of clays with varying proportions of
>Iron. Some of the pots were also slipped with high alumina slips. The kiln
>was fired over 16 hrs. to cone 10, crash cooled to 1000deg.C and clammed
>up. All the pots emerged a pale /concrete grey to beige, many of them with
>good salting and fly ash effects but with very little of the iron tones one
>expected. A selection of these pots was refired over 6hrs in a small
>fibre-lined gas kiln under moderate reduction to Cone 10. All were
>transformed with the beautiful glowing oranges and tans that one looked for
>in the first firing. A mug that was dry grey with no apparent salting came
>out a rich silky brown reminiscent of the classic Dwight or Doulton
>saltglaze surface.
>Has anyone been here before and can anyone explain this phenomenon?
Dear Jim; I think that you would have gotten the result you were after
(warm colors) in your salt firing if you had slow cooled down to say 1600F,
and then cooled faster after that point. To re-oxidize and turn the wares
towards warm tones, the heatwork is better done at higher temps. Your
second fire just gave those wares time to re-oxidize. For my shinos, I cool
the kiln to 2100F and then start it up again at about 1/3 the gas pressure
and hold the fire in oxidation for 3 to 6 hours. The result is generally
'bloody" shino. Hank in Eugene
Vince Pitelka on fri 10 dec 99
At 12:52 PM 12/8/99 EST, you wrote:
>----------------------------Original message----------------------------
>I was recently involved in the firing of a large wood fired salt kiln. The
>pots were made from a wide range of clays with varying proportions of
>Iron. Some of the pots were also slipped with high alumina slips. The kiln
>was fired over 16 hrs. to cone 10, crash cooled to 1000deg.C and clammed
>up. All the pots emerged a pale /concrete grey to beige, many of them with
>good salting and fly ash effects but with very little of the iron tones one
>expected. A selection of these pots was refired over 6hrs in a small
>fibre-lined gas kiln under moderate reduction to Cone 10. All were
>transformed with the beautiful glowing oranges and tans that one looked for
>in the first firing. A mug that was dry grey with no apparent salting came
>out a rich silky brown reminiscent of the classic Dwight or Doulton
>saltglaze surface.
>Has anyone been here before and can anyone explain this phenomenon?
Jim -
This is a pretty common phenomenon in historical salt firing. Brown salt
glaze has generally been preferred by customers over gray, but both are
equally functional. Red ferric iron breaks down to black ferrous iron at
high-fire temperatures, with our without reduction. Quick cooling preserves
it as black ferrous iron, and the clay is gray. Slow cooling allows
re-oxidation to red ferric iron, and the clay is buff and/or brown. So, you
did exactly what you needed to do to get gray saltglaze.
Yesterday we unloaded a gas salt-firing, where I inserted sticks of hardwood
in the firebox while I was salting. Closed the damper upon shutting down
the kiln, and opened it again about four hours later in order to cool in a
reasonable time (heavy hardbrick kiln - big thermal mass!). Got beautiful
browns and buffs. On my own slip-deco rated jars, I got delicious reduction
effects on high-iron slips, in some cases an irridescent black crinkle
finish like often found on antique appliances and camera bodies.
Best wishes -
- Vince
Vince Pitelka
Home - vpitelka@DeKalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
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