Winnie Coggins on wed 6 aug 03
2 vases which were salt fired in a gas kiln grew fuzz on their exterior =
after being used for cut flowers and water. This white growth was =
reported by customers to be 1/2 inch deep. By the time I saw and tested =
the vases (filling with water over night) enough fuzz developed to run a =
finger through but not to measure. After several washings with soap and =
water, this phenomenon disappeared. Both pots had been glazed inside =
and had slip designs but no glaze on the exterior. I assume that there =
was somehow some free salt which grew crystals in the presence of water. =
I think the pots must not be water-tight, even though no moisture was =
felt or noticed on their bases. =20
Both vases are toasty brown, with a visible satin, not orange peel =
surface. Salt burritos were gradually thrown in for 1 1/2 hours =
following a soft cone nine. When cone 10 was down, the gas was turned =
off, usually 30 minutes after the last salt was added. =20
Any explanations? I've tested 15 similar pots from similar firings, but =
these two are the only ones with this "flaw". In future, do I wash all =
with soap and rinse well? Does this speak to potential weakness in the =
glaze surface? =20
Winnie in Columbia, Maryland
iandol on thu 7 aug 03
Dear Winnie Coggins,
Sounds as though you have a cold spot in your kiln if the rest of your =
ware is fully vitrified and did not react this way. In such cases, =
molten salt has wicked into the body before the surface sealed due to =
the fluxing agents in the clay.
I expect you have been taught that the salt you throw into the kiln =
dissociates into Chlorine and Sodium and that there is a reaction with =
water. If so, what follows will probably be regarded as HERESY. =
(Thermodynamic data and calculations support this as do the physical =
properties of the materials mentioned)
Sodium Chloride does not dissociate below about 2500 Degrees Celsius, =
say 4500 F. It decrepitates on contact with a high temperature source, =
flies around the kiln as a powder or as melting particles (NaCl - MP 803 =
C, 1477 F) which fall and impinge on the clay, which should be sticky if =
it has reached maturity. So your Sodium chloride, if not already molten =
will melt, then reacts chemically with anything which is in the vitreous =
phase formed from internal fluxes in our clay. Volatile chemicals which =
are created are discharged. These can include Potassium chloride, =
Aluminium trichloride, Chromic chloride, Ferric chloride and Silicon =
tetrachloride.
But if your clay is not maturely fired it will still have communicating =
voids which will fill with molten salt that can be drawn into the body =
by surface tension and capillary action. Later, in contact with water =
this will leach out, taint coffee in mugs or give you that super =
crystalline growth. Internal reactions may lead to the creation of =
deliquescent salts which absorb moisture from the air and grow =
spontaneously. I know what you are experiencing. I have seen examples =
from my own kilns.
Being a potter or ceramist allows us to lead exciting and interesting =
lives!
Best regards,
Ivor Lewis. Redhill, South Australia
Ron Roy on fri 8 aug 03
Some parts of your kiln are not hot enough - clay not properly vitrified -
salt still soluble - taste it.
Hard to find the cool spots in salt kilns - cones get salted and melt fast.
Maybe try using higher fire cones.
You can do small samples in different areas - those that grow fuss will
tell you where the cold spots are.
Remember - where you need more heat - direct flames to that area.
RR
>2 vases which were salt fired in a gas kiln grew fuzz on their exterior
>after being used for cut flowers and water. This white growth was
>reported by customers to be 1/2 inch deep. By the time I saw and tested
>the vases (filling with water over night) enough fuzz developed to run a
>finger through but not to measure. After several washings with soap and
>water, this phenomenon disappeared. Both pots had been glazed inside and
>had slip designs but no glaze on the exterior. I assume that there was
>somehow some free salt which grew crystals in the presence of water. I
>think the pots must not be water-tight, even though no moisture was felt
>or noticed on their bases.
>
>Both vases are toasty brown, with a visible satin, not orange peel
>surface. Salt burritos were gradually thrown in for 1 1/2 hours following
>a soft cone nine. When cone 10 was down, the gas was turned off, usually
>30 minutes after the last salt was added.
>
>Any explanations? I've tested 15 similar pots from similar firings, but
>these two are the only ones with this "flaw". In future, do I wash all
>with soap and rinse well? Does this speak to potential weakness in the
>glaze surface?
>
>Winnie in Columbia, Maryland
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Tony Ferguson on fri 8 aug 03
Ok, Ivor,
I need you to download all that information on your hard drive brain into
mine. Perhaps we can vulcan mind meld?
What's it going to take to get you to the states for a workshop of some sort
where us lay persons can glean something useful from your myriad of
expertise? Email me off list so we can discuss this please.
Thank you.
Tony Ferguson
On Lake Superior, where the sky meets the Lake
Stoneware, Porcelain, Raku and more
by Coleman, Ferguson, Winchester...
www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "iandol"
To:
Sent: Thursday, August 07, 2003 2:42 AM
Subject: salt fire fuzz growth RR
Dear Winnie Coggins,
Sounds as though you have a cold spot in your kiln if the rest of your ware
is fully vitrified and did not react this way. In such cases, molten salt
has wicked into the body before the surface sealed due to the fluxing agents
in the clay.
I expect you have been taught that the salt you throw into the kiln
dissociates into Chlorine and Sodium and that there is a reaction with
water. If so, what follows will probably be regarded as HERESY.
(Thermodynamic data and calculations support this as do the physical
properties of the materials mentioned)
Sodium Chloride does not dissociate below about 2500 Degrees Celsius, say
4500 F. It decrepitates on contact with a high temperature source, flies
around the kiln as a powder or as melting particles (NaCl - MP 803 C, 1477
F) which fall and impinge on the clay, which should be sticky if it has
reached maturity. So your Sodium chloride, if not already molten will melt,
then reacts chemically with anything which is in the vitreous phase formed
from internal fluxes in our clay. Volatile chemicals which are created are
discharged. These can include Potassium chloride, Aluminium trichloride,
Chromic chloride, Ferric chloride and Silicon tetrachloride.
But if your clay is not maturely fired it will still have communicating
voids which will fill with molten salt that can be drawn into the body by
surface tension and capillary action. Later, in contact with water this will
leach out, taint coffee in mugs or give you that super crystalline growth.
Internal reactions may lead to the creation of deliquescent salts which
absorb moisture from the air and grow spontaneously. I know what you are
experiencing. I have seen examples from my own kilns.
Being a potter or ceramist allows us to lead exciting and interesting lives!
Best regards,
Ivor Lewis. Redhill, South Australia
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Paul Herman on fri 8 aug 03
Hi Winnie,
Two things come to mind.
First, how vitreous or porous is that clay you are using? Some
"stonewares" out there will leak after cone 10 firing.
Second, what's in your customers' water? Is it highly mineralised or do
they use a "water softener"? If so, it would explain the disappearance
of the fuzz when you used YOUR water to fill the vase.
I've heard of Potters using "water softener Salt" to Salt their kilns.
We use "mill run" Salt from the feed store, but it's all Sodium
Chloride.
I've never seen a Salt fired pot grow fuzz!
Do any of the gurus really think that Salt vapor can penetrate the clay
body at cone 9/10 (or even cone 5 for that matter), hang out there and
cool, while remaining water soluble? It sounds improbable. I was under
the impression that those hungry Sodium vapors attached themselves to
SOMETHING in there, (silica?) Grimly and Finally and Forever.
Best wishes,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
>From: Winnie Coggins
> 2 vases which were salt fired in a gas kiln grew fuzz on their exterior
> after being used for cut flowers and water. This white growth was reported
> by customers to be 1/2 inch deep. By the time I saw and tested the vases
> (filling with water over night) enough fuzz developed to run a finger
> through but not to measure. After several washings with soap and water,
> this phenomenon disappeared.
iandol on sat 9 aug 03
Dear Tony Ferguson,
You ask <workshop of some sort where us lay persons can glean something useful =
from your myriad of expertise? >>
Only three things I can think of at the moment with my slow twitch =
brain!!!
A reliable "TransMat Beam", a "Fistful of Dollars" and a willing Spouse.
Best regards,
Ivor Lewis. Redhill, South Australia
=20
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