Ivor and Olive Lewis on thu 18 oct 07
Dear Folk,
Some interesting and unusual topics are turning up in this little =
tribute to Ceramic Arts.
Oct 17 illustrates some very interesting work done with paper clay but I =
am wondering about the reliability of the technical process. =20
This is described as=20
"The vessels are fired in stages. First they are fired unglazed to Cone =
10 in an electric kiln using saggars filled with silica sand to support =
the forms. The stress cracks are filled with slips, glazes, eroded by =
sandblasting or knit together with paper clay as work on each piece =
continues. The work is completed in a small, low-temperature salt kiln. =
Terra sigilattas, slips and glazes are applied with an airbrush, with a =
final coat of sugared water to toughen the surface. The pieces are =
stacked directly touching each other, filling the kiln to enhance the =
flame patterns and texture induced by the reducing salted atmosphere. =
This kiln is fired to Cone 06 over eight hours, reducing heavily after =
800=B0C (1474=B0F) and salted twice above the burners."
Given that the top temperature of the final episode of the process is =
about 1000 deg C, the mp of Sodium chloride is 801 deg C and bp 1413 deg =
C how durable will the final surface be regardless of its seemingly high =
aesthetic value?=20
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Sabri Justin Douglas Ben-Achour on fri 19 oct 07
see if you can contact the lady who made those forms (i don't remember her =
name) and ask. but i know there's been a lot of controversy on clayart abo=
ut how volatile salt or soda are theoretically based on their ideal melting=
points and boiling points versus people's real experience with successful =
salt firing, but i think there are two things to keep in mind.
1. the salt/soda is put in right near the burners or in the firebox, where =
the temperature is a LOT higher than the temperature of the full kiln
2. salt doesn't stay salt at high temperatures, even in a reducing atmosphe=
re. apparently, it forms dimers, rings, and linear polymers that have cons=
iderably higher vapor pressure, entropy, and enthalpy than regular salt. s=
o that explains how it vaporizes so easily and incorporates itself into the=
matrix of the clay.
as i understand it though, it takes a while for the salt to react with the =
clay, but then again she fires for eight hours. my guess is that it is a v=
ery light soda coating but that it is fairly durable. i always thought it =
wasn't really a coating anyway, it's the salt fluxing and incorporating its=
elf into the clay or sometimes the glaze, so i'm presuming its pretty well =
bonded, maybe just fairly thin though.
sabri
www.thesabritree.com =20
> Date: Thu, 18 Oct 2007 16:02:01 +0930
> From: iandol@WESTNET.COM.AU
> Subject: Salt at Cone 06 (Ceramic Arts Dailey - Stress management)
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Dear Folk,
> Some interesting and unusual topics are turning up in this little tribute=
to Ceramic Arts.
> Oct 17 illustrates some very interesting work done with paper clay but I =
am wondering about the reliability of the technical process. =20
> This is described as=20
> "The vessels are fired in stages. First they are fired unglazed to Cone 1=
0 in an electric kiln using saggars filled with silica sand to support the =
forms. The stress cracks are filled with slips, glazes, eroded by sandblast=
ing or knit together with paper clay as work on each piece continues. The w=
ork is completed in a small, low-temperature salt kiln. Terra sigilattas, s=
lips and glazes are applied with an airbrush, with a final coat of sugared =
water to toughen the surface. The pieces are stacked directly touching each=
other, filling the kiln to enhance the flame patterns and texture induced =
by the reducing salted atmosphere. This kiln is fired to Cone 06 over eight=
hours, reducing heavily after 800=B0C (1474=B0F) and salted twice above th=
e burners."
> Given that the top temperature of the final episode of the process is abo=
ut 1000 deg C, the mp of Sodium chloride is 801 deg C and bp 1413 deg C how=
durable will the final surface be regardless of its seemingly high aesthet=
ic value?=20
> Best regards,
> Ivor Lewis.
> Redhill,
> South Australia.
>=20
> _________________________________________________________________________=
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>=20
> You may look at the archives for the list, post messages, or change your
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