Ceramic Design Group on sat 22 dec 01
I have been following this thread for its duration and yes the suggestions
about longer and even slower bisque firings, raising the temperature of the
firings to burn off the offending LOI, all are correct and may help to solve
the problems.
But there is another area in which we can be even more proactive, and that
is learning to ask the right questions of our clay suppliers. If the
suppliers won't answer your questions to your satisfaction, find one that
will.
It seems to me that the majority of list subscribers buy clay in the box
from the major suppliers like Standard, Laguna, Mile Hi, etc. While these
formulae are "carefully guarded" secrets, eg proprietary in nature, you can
ask some pointed questions of your suppliers. You may not be satisfied with
the answers, but at least you can take some steps in the correct direction.
You could ask:
1. When was the most current dilatometry run? Is it run at all? Can I see
the charts?
2. Do you run shrinkage and absorption tests on your clay bodies? How about
on the incoming singular clays?
3. What tests do you perform on each batch of clay that you make, if any?
4. If the bodies have fire clay, do you sieve the fire clay before mixing?
5. Are you using cleaner rather than dirtier ball clays?
6. Do you clean the pre-pug and extruder when changing bodies?
7. Can you recommend users of this clay so I can talk to them about its
characteristics and if it will suit my specific purposes?
8. What are you doing to reduce sulphur in the bodies?
9. Are there any additives to the bodies such as emulsions to increase
plasticity?
10. Has the body been problematic recently? If so, how?
You know, this list of questions is never ending because the nature of the
clay making process is in itself one that cannot be controlled perfectly. No
supplier is willing to take all the necessary steps to provide a defect free
clay body. Well, some do a better job than others. Even making clay in your
studio with the correct equipment will only be as good as the selection of
proper ingredients in the correct proportions and mixed correctly. If the
fire clays are not sieved, then there is a good chance that you can get
bloating or lime related problems. If a really dirty ball clay is used, you
can get pretty obnoxious pin holing in low temperature bodies. And the list
goes on and on.
The point is that we are lucky to get the good results we get, considering
the process and the materials. I only know a few studio operations that can
beneficiate raw materials via slurry mixing, sieving, and filter-pressing.
No matter the size of the operation, it is a significant undertaking both in
terms of labor and expense. We have recently purchased some state of the art
clay making equipment that will reduce significantly our reliance on boxed
clay of dubious formulations. It will increase our labor costs but decrease
or rate of seconds.
If you visit a houseware store and look at the pottery lines, most of them,
in fact all of them, are from white to grey white clay bodies.( White-ware
bodies, porcelaineous-stoneware type bodies) This tells me immediately that
they are using kaolins, clean ball clays, flint, spar pyrophyllite. If the
are slightly darker, then they may have a proprietary clay pit that they
have a red clay from and clean it up before it goes into the mix. Or they
are just using a small amount or iron oxide. Industry wouldn't go near
fireclays and they don't tolerate the kinds of things that potters have been
forced to work with for obvious reasons unless they beneficiate it
beforehand. The suppliers that provide pre-mixed clay bodies for us don't do
this. They might sieve the fireclay, but thats about it. Maybe some
perfunctory testing, etc. I would really like for some of the major
suppliers to share with this list their testing and evaluation procedures
for their house bodies.
Its clearly a case of caveat emptor. But armed with some information gleaned
from reading and asking the right questions, the path may be a bit less
littered with bad clay obstacles. Its an ongoing problem. We read about it
with a great deal of frequency on this list.
Happy Holidays to All!
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
info@ceramicdesigngroup.net
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, Fed Ex,
etc.)
"Custom design and manufacturing for the ceramic arts, giftware and pottery
industries. Molds, models, and tooling for slip casting, jiggering and
hydraulic pressing. Consultation on technical issues such as clay bodies
glazes, and kilns."
Marsh Pottery on sat 22 dec 01
Excellent bunch of questions I've never thought to ask.
That is a "Life Lesson" : To get the answers you need, you have to know
what questions to ask!!
& It's a very hard thing to do when you think about it.
Jonathan wrote about asking your supplier some important Clay Questions:
"You could ask:
1. When was the most current dilatometry run? Is it run at all? Can I see
the charts?
2. Do you run shrinkage and absorption tests on your clay bodies? How about
on the incoming singular clays?
3. What tests do you perform on each batch of clay that you make, if any?
4. If the bodies have fire clay, do you sieve the fire clay before mixing?
5. Are you using cleaner rather than dirtier ball clays?
6. Do you clean the pre-pug and extruder when changing bodies?
7. Can you recommend users of this clay so I can talk to them about its
characteristics and if it will suit my specific purposes?
8. What are you doing to reduce sulphur in the bodies?
9. Are there any additives to the bodies such as emulsions to increase
plasticity?
10. Has the body been problematic recently? If so, how?
Thanks, Jonathan. I'm printing these out to "hit" Roberto at Axner's with
next time I speak to him.. Last batch of stoneware I got there was almost
rock hard & I'm still made about that! Guess they dumped their old clay off
on me because I only buy a couple of hundred LBs at a time. - I throw thin &
it goes far. It's a 100 miles RT or I'd have brought it back.
**Roberto, I hope you are reading this!
Merry Christmas,
Marsha
Dale Cochoy on sun 23 dec 01
----- Original Message -----
From: Ceramic Design Group
Subject: bloating in clays...longish
>
> But there is another area in which we can be even more proactive, and that
> is learning to ask the right questions of our clay suppliers. If the
> suppliers won't answer your questions to your satisfaction, find one that
> will.
, you can
> ask some pointed questions of your suppliers. You may not be satisfied
with
> the answers, but at least you can take some steps in the correct
direction.
>
> You could ask:
> 7. Can you recommend users of this clay so I can talk to them about its
> characteristics and if it will suit my specific purposes?
> 10. Has the body been problematic recently? If so, how?
>
> Its clearly a case of caveat emptor. But armed with some information
gleaned
> from reading and asking the right questions, the path may be a bit less
> littered with bad clay obstacles. Its an ongoing problem. We read about it
> with a great deal of frequency on this list.
> Jonathan Kaplan, president
> Ceramic Design Group
> PO Box 775112
> Steamboat Springs CO 80477
Good info and post Jonathan,
I'll surely ask more before trying a new clay but perhaps just shorten the
questions to the two I snipped out above! :>)
Or, more pointedly..."Does it bloat often?"
The list is GREAT for picking up on this stuff, in fact, that's what got me
off the "What am I doing wrong" attitude and into the "OK, What's wrong with
this clay and does anyone else have this problem?" query
Dale.
Ron Roy on sat 29 dec 01
I also recommend asking your clay supplier about the clays they make. What
harm could it do? On the other hand - if the majority of clay suppliers
have to be dragged screaming into taking some positive steps to ensure
better quality for their product then let's get on with it.
If they are testing ask if they will provide their data - on the clay you
are buying - if it is not done yet can you have the data from the previous
batches.
When I am working with potters on a clay problem - the first question is -
what does our test data show - this is crucial - if the batch looks normal
then the potter is more open to exploring potential problems at their end.
Makes for a better working atmosphere.
If clay companies do not test - or don't show that data then it is easier
to blame everything on the potter - a short term advantage but not good
business in the long run.
In relation to sieving clays before mixing - you would be amazed at what
will show up on a sieve. When clay are dug up - as they all are - unless
they are cleaned during processing - all kinds of debris can get mixed in -
broken glass for one thing.
The recommended sieve size is 30 mesh by the way - pieces of calcium carb
smaller than 30 mesh will not pop.
RR
>You could ask:
>
>1. When was the most current dilatometry run? Is it run at all? Can I see
>the charts?
>2. Do you run shrinkage and absorption tests on your clay bodies? How about
>on the incoming singular clays?
>3. What tests do you perform on each batch of clay that you make, if any?
>4. If the bodies have fire clay, do you sieve the fire clay before mixing?
>5. Are you using cleaner rather than dirtier ball clays?
>6. Do you clean the pre-pug and extruder when changing bodies?
>7. Can you recommend users of this clay so I can talk to them about its
>characteristics and if it will suit my specific purposes?
>8. What are you doing to reduce sulphur in the bodies?
>9. Are there any additives to the bodies such as emulsions to increase
>plasticity?
>10. Has the body been problematic recently? If so, how?
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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