Dannon Rhudy on thu 20 nov 97
Stuart, it sounds like your lids and casserole walls are not the
same thickness. This is a fairly commmon problem, and will cause
one or the other to shrink differently. Also, you should place
the lid into the casserole gallery as soon as it is stiff enough
to do so. If you are concerned about the two sticking together,
you can place a thin paper towel or some other thin flexible
paper between the two edges.
It might be easier to adjust/check for/ thickness if you threw
your lids upside down, and added a handle later. It would
actually save you a lot of trimming, anyway. It is easier and
faster to attach a handle (thrown on or off the lid itself) than
to trim the gallery edge of the lid.
Dannon Rhudy
potter@koyote.com
----------------------------Original
message----------------------------
Every time I make large casseroles, I have the same problem: my
lids don't
fit. This is not just a matter of random sloppiness, because the
misfit is
always in the same direction: the lid is too large. Furthermore,
I measure
both casserole and lid to the millimeter, and I check my
measurements over
and over. Is this a common experience? Can anyone explain it?
Some information that may help:
1. I throw the body and the lid from the same wedged ball of
stoneware
clay.
2. I throw the lid right side up. That is, I throw a torus of
clay, then
pull the wall toward the center until it closes over, then throw
the handle
from the excess clay in the middle. At the leather hard stage,
the bottom
and sometimes the top are trimmed in a clay chuck.
3. Sometimes the body when dry is slightly asymmetric, having
shrunk more
in one direction, so that it is wider in one direction than at
right angles
to that direction. Yet, my lids are usually larger than even the
long axis.
4. I make the lid (when wet) about 3 mm narrower than the top of
the body,
so that there should be a small gap around it when it is seated on
the body.
5. The bottom of the casserole is heavily compressed by the large
flat rib
that I use to flatten and level it. Could this affect its
shrinkage?
6. Are my tolerances unreasonable? Should one allow for a larger
gap
around the lid of a larger casserole? My casseroles are typically
250 to
300 mm. Well, 2.5-3.0 mm is just 1% of that.
7. Last year, I made a large casserole from Laguna Clay's Big
Pot, which is
a well-grogged throwing clay. The lid fit! Coincidence? Or does
the
extra grog reduce not just shrinkage but variability in shrinkage?
Any ideas or advice will be appreciated! I'm getting tired of
trying to
trim dry lid edges!
Stuart Altmann
KarateHiro on tue 2 dec 97
>Every time I make large casseroles, I have the same problem: my lids don't
>fit. This is not just a matter of random sloppiness, because the misfit is
>always in the same direction: the lid is too large.
Sounds like one-sided "conundrums", the term which caught my attention to this
post. My answer is simple.
If the lid is too large, make it smaller. If you are crafty enough, this should
solve the problem and give you lords of pleasure when the lids fit perfect.
Voila! What's the problem?
The hidden problem I guess is the randomness of size discrepancy, if such a
thing exists.
>Furthermore, I measure
>both casserole and lid to the millimeter, and I check my measurements over
>and over. Is this a common experience? Can anyone explain it?
>
Before sharing my experience. A disclaimer: about ten years ago, I was
fascinated by this subject of varying shrinkage as related to the shapes
thrown, and embarked on a comprehensive treaties on it (like CM article
candidate) and then abandoned the project. Lot of things in life don't fit or
measure up. So why bother?
Since no one dared answer the originally posted question (ten days ago), let me
give you a quick rundown for what's worth..
The shrinkage is little discussed, but very common subjects observed by
functional potters (like someone who throws stoneware casseroles). Being
analytically minded, I asked a lot of questions, but received little precious
pseudo-scientific or experiential answers, at least nothing definitive, on this
subject. I swear.
It seems that high-fire clay bodies shrink as much as 18%, since the space
between clay molecules gets compacted and the clay gets realigned, etc,, once
fired. That is a very scientific answer, isn't it? Will do it for now.
The shrinkage affects, not uni-directionally, but obviously in a
three-dimensional fashion. The thnner lids tend to "sit up", depending on how
flat they are. And the bottom obviously shrink at a different rate and not in a
two-dimensional plane. Whatever the yardstick or footstick available that you
may use, that's what normally takes place..
Practically speaking, the aesthetics of elegant greenware shapes as in
multi-stage platters with sharp slopes are hard to maintain, once fired. What's
good looking as greenware seldom stays the same if bisqued or glaze fired. I
guess all these are common knowledge among functional potters. It was evident
to me even as a novice potter. So, let us take a guess. That is why you have
not received any direct responses (barring busy crafters, etc.). So obvious.
And they solve the problem in their own fashion, suited to their style and
needs.
One solution I have arrived at is to throw the lid fairly deep, then, the fit
and shrinkage tend to stay about the same with less variations. The cutomers
can use both the lid and the bottom for two different purposes, if they choose
to. And that style was my trademark at one time. Less so today, but my
woodblock printing advertising still shows that shape. No copying, mind you.
The truth was that there was not much enthusiastic acceptance for that type of
beauty. The customers, or more precisely, the prospects, the potential
customers, were not quite that advanced or ready. A lot of persuation was
needed. The casseroles looked great, though. To me at least. And to a lot of
others. But that is another story.
The shape was unique, different, and better (to me, at least). I am a good
cook, you see. So I was convincing.
Hiro Matsusaki
P.S. The most practical way to solve the problem is simply to throw multiple
bottoms of the same size and lids wtih slightly varying diameters and shapes in
the hope of matching them up. The detailed techniques vary, but the idea works.
A lot of functional potters will advocate it or its derivatives. But again, who
wants to make all those casseroles the same size? People's appetites vary, and
the size of their stomach can shock you. But they want a reasonable appearance.
HM
KarateHiro on wed 10 dec 97
>our Clayart message re lids. I have been intending
>to send the same question. I am having the same problem!!!:^(
>Although a long experienced thrower, suddenly my casseroles are really
>holding up production and completely wrecked my wholesale market this
>season. I can't get the damn casserole orders out. Only about 1 in a set
>of 5-6 will have a lid that fits by the time they are dry enough to trim.
>
I thought I gave my penny'sworth on this subject. The shrinkage rates vary by
clay bodies. Everyone should know this, if in functional production bit. The
range is between 13 to 18 percent, officially or scientifically, but could be
more or less, depending on how you throw and fire. In medium fire, the
shrinkage is far less, so this could be a factor in this discussion.
>I was so glad to see your Clayart message re lids. I have been intending
>to send the same question. I am having the same problem!!!:^(
>Although a long experienced thrower, suddenly my casseroles are really
>holding up production and completely wrecked my wholesale market this
>season. I can't get the damn casserole orders out. Only about 1 in a set
>of 5-6 will have a lid that fits by the time they are dry enough to trim.
The clay bodies have different shrinkage rates. We all should know this, if we
are in the functional prodction bit. Only that it affects those who are in
more advanced stage or more experienced, and the time makes us forget the
shrinkage business, all too common and not noticed for ordinary production.
Please refer to my previouspost on this subject. If it does not help, someone
else could certainly do. I am sure. My own solution could not possibly apply to
everyone else.
Hiro Matsusaki
Hiro Matsusaki
"Where things can be in homeostasis, in a state of balance, most of the time,
but not always>:-)." A haven for the budget traveler.
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