David W McDonald on wed 25 aug 99
Hi Ron,
Please accept my sincere thanks and gratitude for taking the time
and energy to respond to me in such an informative and enlightening way.
I hope your message went to clayart as well, as I'm sure others would be
glad for it.
Ron, contrary to what you say near the end of your message, this
IS what I wanted to hear. Deeper understanding and information on all
fronts. As to your thoughts that it should be possible to successfully
fire this clay to a full cone 10 without bloating, since there is no
slumping, I fully agree. It's just that I haven't yet found the way to do
it, and what was a well trodden path through a long familiar forest (I
successfully fired the "Amador" clay body, without problem for 19 years),
suddenly changed to a very narrow and unfamiliar path through a dark
wood. With your detailed information however, I'm sure I could now
possibly find my way back to a successful route. Most interesting
information you offered. I'll definately consider it all!
I Saw Tuckers Pottery Supplies ad in Ceramics Monthly. I'm
guessing that's your picture taking notes behind all those test bars. I
was immediately struck by the large caption in the ad: "Confidence". What
an important word to me at this moment. What a concept!
I sure wish Tucker's clays were available here in the Southwest U.S.
I found a clay body producer in Albuquerque, New Mexico ( Ceramic
King/ New Mexico Clay is what they're called) that has only one pug mill
and only offers a few of their own bodies (they also carry Laguna's
clays). One of them, which they call "Anasazi", is very similar to
Laguna's Amador in appearance. I started introducing it into my studio
and testing it about a month ago. The results are wonderful, so far. It
works well with my glazes and fires to cone 10 fine. No signs of
bloating. One of the things I've found most surprizing about it is how
smooth all the glazes come out now. For a few years now, my glazes, which
include saturated iron tenmokus and rutile blues, have commonly come out
of the kiln (in some places) a bit rough and pitted, like many small
blisters or pinholes. My work is mostly decorative, and the roughness of
the glazes I speak of are not that bad, but it is noticeable. However, on
the clay from Albuquerque, the glazes are spectacularly smooth! Which of
course leads me to think that it was something about the Laguna clay I
was using which contributed to the roughness of the glazes. My friend in
Durango, Nick Blaisdell, found the Ceramic King source. He had been
having miserable luck with blisters and pinholing for the last couple of
years ( we figured out that it was right around the time that Laguna
switched sand suppliers), especially with rutile blues. In years past he
had no such problem. His wife and he work together. He does the firings
and she the glazing. So of course for the last 2 years since the
pinholing started, he has really gotten alot of grief from her (not that
he liked it either). Surely they thought, he just didn't know how to fire
a kiln anymore. And now, since switching clay and suppliers, the
pinholing and blisters all went away! What do you think about that? Could
the sand which has apparently contributed to my (and Nick's, and others')
problems with bloating, also have been causing more volatility in the
glazes?
I'm not meaning to overload you with more requests already Ron,
so answer when you feel like it and have the time, OK? Thanks again.
David McDonald
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June Perry on thu 26 aug 99
Dear David:
Glad you posted that. I was using Amador and Rod's Bod years ago with nary
every a problem with pinholing on most glazes. I was reducing very early for
good shinos, doing low bisque (cone 08) and still didn't have problems except
the occasional pinholes with the ghastly borate chun.
A couple of years ago I started having problems with some of my glazes. I
went round and round here on Clayart with lots of good info from Ron Roy and
others and I tried it all. I went to distilled water just in case my well
water was the culprit. I upped my bisqued and didn't start reduction till
much later, spaced my pots a little further apart, and fired very slowly and
still had pinholes. I never thought at the time it was the claybody! I'm glad
to hear that it is probably from the clay and not anything I suddenly started
doing wrong!
Maybe we can get Ron to talk his company into a U.S. West coast dealership.
It sure looks like there is a big hole here that could be filled by someone
with integrity and good business habits and good clayforming techniques,
testing, etc. :-)
If I was younger, I'd rent some industrial space and go into the claymaking
business and hire Ron Roy as my consultant and materials tester! :-)
Right now I'm going through a lot of body testing and will probably make some
or all of my own clay. I have all the necessary machinery and I'm retired so
I can afford the time, although there never seems to be enough of that with a
retired, wants to be entertained, husband at home.
Warm regards,
June
Ron Roy on thu 26 aug 99
Hello again David - yes that is me in the Tucker add - they made me wear
the lab coat - just for one shot I said - and of course thats the only one
anyone gets to see - well never again - well maybe if they can afford it.
If there are pin holes and craters - that do not heal over at least
somewhat in a second firing you are probably dealing with overfired clay
which is beginning to break down - producing gases under the glaze. This
can be the result of too fast bisque firing and/or not enough oxygen in the
crucial stage of bisquing between 700C and 900C - particularly with iron
bearing clays. The reduced iron in these bodies becomes a flux starting at
about 900C - so the fault can affect the full range of common studio
firing. More so at top temperatures of course - but it happens in oxidation
as well as reduction firings. The bits of iron in fire clays can be
involved - and may be the source of the problem even in near white bodies.
I have never seen the problem in porcelain.
I can also happen if a clay in not refractory enough for the top rated
temperature but the clay blistering (bloating) will be uniform over the
whole pot - not localized.
It is a rather simple test - to find out if you have excess oxygen in your
kiln - electric or gas fired - simply insert a piece of combustible -
cardboard or wood will do - into the kiln. If it burns inside the kiln
(between 700C and 900C) there is oxygen present.
Those firing with gas - or any fuel for that matter - make sure burners are
adjusted for excess oxygen - just keep testing for free oxygen till you are
sure it's there. The setting will change depending on the weather so you
need to educate yourselves about your kilns and burners and dampers. The
worst situation would be to find your kiln had slipped into reduction
during a crucial stage of a bisque firing - once that iron is reduced to
FeO it is very difficult to reoxidize it - no matter how high you bisque
and how long you soak.
It is a rather simple test - to find out if you have excess oxygen in your
kiln - electric or gas fired - simply inset a piece of combustible -
cardboard or wood will do. If it burns inside the kiln (between 700C and
900C there is oxygen present.
The habit of cranking kilns on full after red heat is just not the right
thing to do in most cases. You want no more than a 100C rise per hour -
more in some cases of thick ware made with dirty clay. That means about 11
hours for a cone 04 bisque. Best to leave a spy hole open to encourage some
air flow. Those with vent systems - which supply fresh air through out the
firing can go faster of course - but you can still test for free oxygen if
you want.
Just remember - clay bodies are made of stuff dug up - even the most
innocent looking clay can have much more contamination then the load before
- the people who make your clay have no idea what is going on till the
complaints start coming in. Even those that do test every batch - the clay
is probably gone before the testing is finished. And it can happen if you
are mixing your own clay - especially if you are not testing the raw
materials and the finished body. Proper firing techniques can certainly
help as well - just remember - fast firings create more problems than they
cure - the opposite for slow firings.
David - I did not post the comments I sent you to the list - If there are
those who would like an edited version - just let me know - what I have
said above is the basically it.
David said - snip"
>One of the things I've found most surprising about it is how
>smooth all the glazes come out now. For a few years now, my glazes, which
>include saturated iron tenmokus and rutile blues, have commonly come out
>of the kiln (in some places) a bit rough and pitted, like many small
>blisters or pinholes. My work is mostly decorative, and the roughness of
>the glazes I speak of are not that bad, but it is noticeable. However, on
>the clay from Albuquerque, the glazes are spectacularly smooth! Which of
>course leads me to think that it was something about the Laguna clay I
>was using which contributed to the roughness of the glazes. My friend in
>Durango, Nick Blaisdell, found the Ceramic King source. He had been
>having miserable luck with blisters and pinholing for the last couple of
>years ( we figured out that it was right around the time that Laguna
>switched sand suppliers), especially with rutile blues. In years past he
>had no such problem. His wife and he work together. He does the firings
>and she the glazing. So of course for the last 2 years since the
>pinholing started, he has really gotten alot of grief from her (not that
>he liked it either). Surely they thought, he just didn't know how to fire
>a kiln anymore. And now, since switching clay and suppliers, the
>pinholing and blisters all went away! What do you think about that? Could
>the sand which has apparently contributed to my (and Nick's, and others')
>problems with bloating, also have been causing more volatility in the
>glazes?
> I'm not meaning to overload you with more requests already Ron,
>so answer when you feel like it and have the time, OK? Thanks again.
>David McDonald
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Craig Martell on thu 26 aug 99
Hello David:
I've read all of the posts about bloating. I definitely think that it's
the claybody. Everything you've done and every avenue that you've taken
has indicated that it's the composition of the clay. Pieces don't
necessarily slump when bloating occurs and the less than 1% absorbtion
factor certainly points to over vitrification.
My wife used a cone 6 body that bloated when cone 6 was in the 3 o'clock
position. No slumping. She was also getting some of the glaze blisters
and roughness you mentioned. I called the supplier, which is not Laguna by
the way, and talked to them about it. The response was: "That body is
just tempermental". I said that it was poorly formulated and they should
reformulate it or stop selling it as a cone 6 clay. She changed clays and
suppliers and she now has no bloating and no pits, blisters, or roughness.
You've been through a rough patch and I empathize. I'm glad though that
you've found a clay that works for you and your glazes are working better
as well. I also feel that Laguna owes you some compensation but I'm just a
schmuck from Oregon and exert no influence. The only thing that any of us
can do is deal with companies that make and sell good products and treat us
fairly. I'm not making a judgement call on Laguna by saying this but I
don't think I'd use any of their clays without some serious testing. I mix
my own anyway! :>) Lotta work but if anything gets screwed up it's my
fault and I don't have to be pissed at anyone.
wishing you good pieces, and good firings, Craig Martell in Oregon
Nils Lou on thu 26 aug 99
June and others--I believe that Ron Roy already consults on clay with
Axners of Florida. I have seen their production setup and it is well
organized. Two other places that do a conscientious job are Clay Arts in
Tacoma and Continental Clay in Minneapolis. Nils
On Thu, 26 Aug 1999, June Perry wrote:
> ----------------------------Original message----------------------------
> Dear David:
>
> Glad you posted that. I was using Amador and Rod's Bod years ago with nary
> every a problem with pinholing on most glazes. I was reducing very early for
> good shinos, doing low bisque (cone 08) and still didn't have problems except
> the occasional pinholes with the ghastly borate chun.
> A couple of years ago I started having problems with some of my glazes. I
> went round and round here on Clayart with lots of good info from Ron Roy and
> others and I tried it all. I went to distilled water just in case my well
> water was the culprit. I upped my bisqued and didn't start reduction till
> much later, spaced my pots a little further apart, and fired very slowly and
> still had pinholes. I never thought at the time it was the claybody! I'm glad
> to hear that it is probably from the clay and not anything I suddenly started
> doing wrong!
> Maybe we can get Ron to talk his company into a U.S. West coast dealership.
> It sure looks like there is a big hole here that could be filled by someone
> with integrity and good business habits and good clayforming techniques,
> testing, etc. :-)
> If I was younger, I'd rent some industrial space and go into the claymaking
> business and hire Ron Roy as my consultant and materials tester! :-)
> Right now I'm going through a lot of body testing and will probably make some
> or all of my own clay. I have all the necessary machinery and I'm retired so
> I can afford the time, although there never seems to be enough of that with a
> retired, wants to be entertained, husband at home.
>
> Warm regards,
> June
>
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