Rimas VisGirda on sun 15 aug 10
In the 60's we saltglazed in the Sierra foothills and I was not concerned w=
ith the denser than air discharge from our stack... In my early teaching du=
ring the 70's and early 80's I built salt kilns in urban situations and did=
some research into the discharge to allay university fears. If memory serv=
es, my results were as follows, the original papers are buried someplace in=
my accumulated paper files, if even they exist any more...
We started salting at about cone 6, salt did not appear to be reactive with=
the clay until those temperatures. At c/6 NaCl as it enters the hot atmosp=
here disassociates into Na and Cl ions. The Na attacks the clay to combine =
with the silica content and thus forms some type of sodium silicate (glaze)=
on the surface of the clay. The chlorine is very reactive and combines wit=
h the (secondary?)air (80% Nitrogen, 20% Oxygen) entering the chamber to go=
through various reactions producing HCl (gas), also very reactive, and ult=
imately NH4Cl (ammonium chloride). NH4Cl is a dense, white, heavier than ai=
r gas, it is also used to produce "smoke" in theater productions, although =
by different means... The above reactions revolve around the production of =
Cl2 (chlorine gas) and HCl (hydrochloric acid gas) at the high temps inside=
the kiln and are very fast with essentially no release of (poisonous) chlo=
rine gas into the atmosphere. Any HCl gas, if any, is minimal and
the rusting you might see on nearby iron is most probably a result of wate=
r vapor and hot exhaust to accelerate rusting and not to hydrochloric acid.=
..
As I said, I found the above conclusions more than 30 years ago and don't h=
ave reference now to my sources. Back in those early days I was interested =
in the physics and chemistry of clays and firings and attended ceramic engi=
neering seminars whenever I had the chance... I'm no longer interested in p=
ursuing those topics although it's, occasionally, interesting to read about=
them in the clayart digest I get each morning...
THE SALTY STORY
In the 60's and early 70's Dick Hotchkiss and I ran a small pottery busines=
s in the Sierra foothills (Grass Valley). We dug our own clay and fired wit=
h wood, for economic reasons, not aesthetic. We also played around with var=
ious kiln designs as well as salt glazing. We took commission orders from a=
candle maker in the valley for something we called candle-pots; these were=
a small 2 inch high by 4-5 inch diameter pot that we fired lip to lip and =
foot to foot i anywhere from 1.5 to 2 foot stacks. At this time we had 2 fu=
nctioning kilns, and one was a salt kiln. Our reduction kin was still cooli=
ng and we needed to bisque about 1000 of the candle-pots to get them glazin=
g and ready for the high fire, so we bisqued them in the salt kiln. We bisq=
ued by eye to not much over red heat -a nice dull glow like you would get f=
rom the ember on the end of a cigarette. They fired just fine and we got th=
em glazed and loaded into the other kiln in the typical 1.5-2 foot
stacks and fired to cone 10-11. When we opened the kiln we had 2 foot colu=
mns of (salt) glazed together candle-pots... Apparently bisquing in the sal=
t kiln introduced enough salt into the clay to form enough of a self-glazin=
g clay to stick everything together. I've forgotten if we tapped or pried t=
hem apart and polished the lips and feet or whether we chucked them -it was=
an interesting 1000 pot experience...
-Rimas
Ann Brink on sun 15 aug 10
What a story! I can hear it now: "HOOOOLY S#$%!!!!
Ann Brink in Lompoc CA.
> THE SALTY STORY
>
> In the 60's and early 70's Dick Hotchkiss and I ran a small pottery
> business in the Sierra foothills (Grass Valley). We dug our own clay and
> fired with wood, for economic reasons, not aesthetic. We also played
> around with various kiln designs as well as salt glazing. We took
> commission orders from a candle maker in the valley for something we
> called candle-pots; these were a small 2 inch high by 4-5 inch diameter
> pot that we fired lip to lip and foot to foot i anywhere from 1.5 to 2
> foot stacks. At this time we had 2 functioning kilns, and one was a salt
> kiln. Our reduction kin was still cooling and we needed to bisque about
> 1000 of the candle-pots to get them glazing and ready for the high fire,
> so we bisqued them in the salt kiln. We bisqued by eye to not much over
> red heat -a nice dull glow like you would get from the ember on the end o=
f
> a cigarette. They fired just fine and we got them glazed and loaded into
> the other kiln in the typical 1.5-2 foot
> stacks and fired to cone 10-11. When we opened the kiln we had 2 foot
> columns of (salt) glazed together candle-pots... Apparently bisquing in
> the salt kiln introduced enough salt into the clay to form enough of a
> self-glazing clay to stick everything together. I've forgotten if we
> tapped or pried them apart and polished the lips and feet or whether we
> chucked them -it was an interesting 1000 pot experience...
>
> -Rimas
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