Stephani Stephenson on sat 6 jul 02
Hi Elizabeth
This is a shot in the dark as
1) I don't know where you are, who your supplier is..
2) I don't really know how 'fragile and delicate' your 'fragile and
delicate' is , and whether it is pushing the limits of what any clay can
successfully do .....but here are some thoughts which come to mind,
hope they might be of help!.
1.Is it possible this is a design problem ? Is the cracking occurring
because you have very thin frog toes attached to a thicker piece (thin
toes attached to thicker part of vessel or sculpture.) Is there anyway
you can make the transition from thick to thin less drastic and more
gradual? Are the thin parts bridging a gap? i.e. a slender toes
suspended in space, with air on all sides ? Have you thought about
putting a small 'pillow ' of clay under the fragile parts, sort of a
'removable support that can be gently removed after bisquing? (again, I
don't know how small these are!) Put a barrier such as paper between
the 'toes' and the 'supports' to facilitate removal.
The supports, which are clay surrounding the fragile parts, will also
help slow down the drying of the toes as well as provide structural
support, and they will have same % shrinkage.
2. What about beefing up the fragile toes , but making the beefier
part not so visible? For example instead of having a projecting piece
shaped like a long skinny letter "I" , think of an inverted "V" shape,
with the tiny part still visible , but a wider base underneath.
3. what about using 2 part epoxy for the toes? (this may be
inappropriate for your pieces and glazes , but who knows!!!) I have
used this for fragile extensions, such as tiny ribs , etc. East Valley
epoxy is great and wonderful things can be done with their pigments as
well.
4. One sculpture clay I have used which has good working properties,
can go to cone 6, and seems to have a smaller grog size than many is
WSO, a whitish clay from Laguna. It may still contain too much grog for
your needs but might be worth a try. Also you mentioned you prefer red
clay..., possibly could put a red slip made from your clay over the
WSO???
anyway for what it's worth! Good luch with the little creatures!
Stephani Stephenson
Carlsbad CA
Elizabeth Hewitt on mon 8 jul 02
Thanks Stephani, Snail and all the good members who have once again so
freely given information and advice. One last question for the sake of
the little frogs that are greenware waiting to be fired.
The last ones that I had sculpted before getting your advice but not
fired yet have tiny wire armatures in their feet and their toes were
built upon them. I see fine cracks in the clay where some of the toes
meet the foot. I plan to fire them, what have I got to lose but for them
and any future sculpting of any kind, I would like to understand the
effects of the fire on the steel armatures. In reading about the
melting temperature of steel, it sounds like it melts at 2500+ F. Our
family owned business, non pottery related, works with steel, brass and
other metals. I don't work with that end of it but the financial. My
hubby tells me that the melting temperature for steel is higher than my
cone 6 firings..which is in line with the temperature above. Has anyone
seen this first hand? If that is accurate, I have hopes that these
little guys will be safe. In a few days I will know first hand but like
to minimize my surprises/shocks. It's hard not to get attached to these
lil guys who each seem to take on a spirit/personality of their own.
Thanks again,
Elizabeth, ye ole froggie maker.
Dannon Rhudy on mon 8 jul 02
>
>The last ones that I had sculpted ...
have tiny wire armatures in their feet and their toes....
Generally speaking, clay built directly upon solid armatures
will crack during drying and firing. The clay is shrinking
all the time, the armature is not. Since the clay cannot
shrink THROUGH the armature - it cracks. There are some
times when this might not happen (paper clay has a lesser
tendency to crack around fine armatures) but on the whole
clay requires special(shrinkable/compressable)armatures.
regards
Dannon Rhudy
Snail Scott on mon 8 jul 02
At 05:08 AM 7/8/02 -0400, you wrote:
>[little frogs]...
>have tiny wire armatures in their feet...In reading about the
>melting temperature of steel, it sounds like it melts at 2500+ F.
I have seen steel fired in kilns, but never
when fully encapsulated in clay, so my
experience may not be precisely applicable,
but since the clay coating is so thin, it
may not make much difference. So, a few guesses:
Although steel doesn't melt at stoneware temps,
it does oxidize, and form a noticeably thick
surface coating. I would fear that any such
oxidation could cause stresses in the tiny toes.
The clay layer may protect the steel, but I
don't know.
Steel also loses much of its hardness and
strength at these temperatures. This may be
less relevant, though, since although the
gauge of the wire must be small, the length
probably is, too, so if there isn't too much
(relative) weight on the ends, they may not
deform too much. Only experience will tell.
Clay continues to shrink during firing, while
steel will not. If you already have cracking
due to the shrinkage differential, I fear it
may worsen in firing.
Can you make the toes without the armature?
Or perhaps try a little fiber reinforcement
for green strength. Too much fiber will
compromise the fired strength, but a little
may help the toes survive long enough to be
fired. If possible, though, I'd do without
any armature at all.
I used to do really tiny stuff, and for the
ridiculously small parts, I let the porcelain
stiffen and even dry, then used pins and
cut-down dental tools to carve and refine the
form, adding just a tiny droplet of water
where needed to aid the process. Then I would
paint the delicate parts with white glue to
help protect them until firing. (That was
quite a while ago, and I haven't done it much
since. Possibly another, harder coating
material would be even better. Maybe shellac?)
-Snail
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