Kate Johnson on sat 25 dec 04
...well, not really, but I AM glad to see that there are others of you out
there writing ClayArt, so I don't have to feel guilty doing so.
I'm SO frustrated. I made a batch of nice marbled slipware pieces a few
days ago, using plates for molds (by the way the Pam is a GREAT suggestion,
thank you!). I think these were the nicest ones yet...
As usual, timing is EVERYTHING in working with clay, and mine was off.
First, I goofed by decided to go with the experts (I think that might be
part of the problem, anyway!)--most of the books on the subject of slipware
suggest allowing things to dry overnight to leatherhard before marbling,
etc. Normally, I do it immediately, because it seemed logical to get a
better fit that way, but...decided to follow directions. Maybe not the best
idea I ever had. The rims were slightly dryer than the bases, BEFORE
slipping, even though I'd covered them well overnight
So, the next day added the slip...tried to keep drying even by covering
everything with plastic again, but managed to ding one plate's surface and
didn't know it till the next morning--the slip is VERY delicate at that
stage. So. Scraped that one level on day three and started again with
fresh slip, as the books suggest. Edges now significantly dryer than the
newly-wet bases, though. Tried again to slow and even the drying, but...
The larger marbled plate just got a fairly thick, complex layer of slip--no
significant problems that I knew of with that on. It looked GORGEOUS--till
I took it out of the mold to trim it this morning and discovered a crack,
almost all the way around the base, on the back. Ah well...mosaic bits. Or
if it holds together, maybe a wall hanger....though the crack now shows
through to the face, after a couple more hours.
The other problematical marbled plate, the one that got dinged under its
plastic, is now developing a hairline crack...siiiiigh.
Interestingly, the platter I made in my plaster mold looks great, no
problem. (So far.) Ditto the large plate I just completed a complex
sgraffito on...no idea why it's behaving, I had to rinse it off, too,
because the slip was a bit thick and didn't go on evenly. So fingers
SERIOUSLY crossed, there, lots of work in that sgraffito...
My take on the problem is uneven drying, too much difference in moisture
between the slip and the ware, and perhaps not enough Pam on the two with
the problems. The 3-colored one had stuck on the bottom, a bit, and I
noodged it loose. Carefully, I thought, but it's the one with the huge
crack.
I'm definitely in the market for wallboard to dry these things on, in the
hopes of equalizing the base/rim ration of moisture...
Also considering my old friend Mr. Hairdryer, for drying the bases a bit,
keeping the rims protected.
Opinions, please?
And by the way, thank you for the advice on the plaster mold, it's behaving
like a champ, now! NO problems, there!
And a very merry Christmas to all here...you've been a real gift to me.
Regards,
Kate Johnson
Graphics/Fine Arts
http://www.cathyjohnson.info/
http://www.epsi.net/graphic/
http://www.ebsqart.com/Artists/cmd_1494_profile.htm
patti yager on sun 26 dec 04
Hi Kate,
A couple of years ago, while apprenticing, I had the same problem trying to
make porcelain luncheon plates using a plastic plate as a mold and WD40 to
release. Those plates cracked all over the place and I finally gave up. And
the cracks started on the bottom. As I read your description it occurred to
me that the release agent may be the problem, causing uneven drying as it
covers the bottom surface.
Hope this solves the problem for both of us!
(mud)Patti
Kate wrote:
significant problems that I knew of with that on. It looked GORGEOUS--till
I took it out of the mold to trim it this morning and discovered a crack,
almost all the way around the base, on the back
Kate Johnson on sun 26 dec 04
Hi Patti--
>
. As I read your description it occurred to
> me that the release agent may be the problem, causing uneven drying as it
> covers the bottom surface.
> Hope this solves the problem for both of us!
I do find that the bottom stays much damper--the plate shrinks away from the
rim and the edges get much dryer, but that flat bottom stays much wetter,
particularly when marbling with multiple colors of slip.
Interestingly, the first batch of stuff I did with Pam as a release agent
had NO problems, at all. I'm trying to remember what I might have done
differently. One thing was that I was actually MORE generous with the
Pam...it was pretty slick and the plates and bowls seemed to want to slide
out while I was applying the slip--it was pretty tricky. I'm wondering if I
also took them out of their molds sooner, and if so why I didn't have more
problem with them warping. ?!?!
So far the large, slipped, sgrafitto plate looks fine...no cracks at all,
and I did it the same way, or so I thought. Oy...
And ACK, I am OUT OF CLAY, so can't experiment any further till I can get to
the supplier this week...or snag my last box at school tomorrow. Thought I
had more!!
Thanks for the food for thought...
Best--
Kate
Snail Scott on sun 26 dec 04
At 08:53 AM 12/26/2004 -0600, you wrote:
>Interestingly, the first batch of stuff I did with Pam as a release agent
>had NO problems, at all...I'm wondering if I
>also took them out of their molds sooner, and if so why I didn't have more
>problem with them warping...
PAM will probably slow drying somewhat, but leaving
it in the waterproof mold will seriously slow the
drying, and the edges will dry disproportionately
faster in the meantime. Unmolding too soon will cause
bending, but uneven drying will cause warping, too,
and it's harder to correct for.
First thing: get it out of the mold as soon as the
form will support itself. If you can't, place a strip
of dry-cleaning plastic around the rim to keep it
equally damp. Consider doing this anyway.
Long-term: consider making plaster press-molds from
your glassware. Plaster will allow the work to dry
more evenly and quickly. You could probably decorate
the work almost immediately if you used plaster molds.
-Snail
Kate Johnson on sun 26 dec 04
Hi Snail...
>
> PAM will probably slow drying somewhat, but leaving
> it in the waterproof mold will seriously slow the
> drying, and the edges will dry disproportionately
> faster in the meantime. Unmolding too soon will cause
> bending, but uneven drying will cause warping, too,
> and it's harder to correct for.
Thanks, I'm sure that was part of the problem. The John Pollex book on
slipware talks about having to have an assistant when you take larger
plates, etc. out of the mold (I believe he said 12"-13"), and I can see how
that would be helpful, to support the form as much as possible. Not an
option when you work alone, of course.
>
> First thing: get it out of the mold as soon as the
> form will support itself. If you can't, place a strip
> of dry-cleaning plastic around the rim to keep it
> equally damp. Consider doing this anyway.
Would have been a better option than what I did, which was cover the whole
with a plastic bag...that was how I managed to ding the marbling without
knowing it till the next day. That stuff is incredibly delicate, and
there's no "fixing" it. I had read you could allow it to dry and then use a
metal rib on it...not so, it just smears and loses definition. Will try the
edge wrap, if I can't get the thing out of the mold quickly enough...
>
> Long-term: consider making plaster press-molds from
> your glassware. Plaster will allow the work to dry
> more evenly and quickly. You could probably decorate
> the work almost immediately if you used plaster molds.
And DO, actually! This is my pottery-in-progress album, you can tell the
plaster-molded patter is still quite wet when I added the marbling.
http://pg.photos.yahoo.com/ph/graphicartepsi/album?.dir=bbb8
I bought more plaster the other day, with just that solution in mind--the
larger ones are terrifically heavy, especially when full of wet clay and
slip--I had *very* quivery muscles lifting and tilting all that to marble
it! But I haven't had a single failure (YET, knock wood!) with the plaster
molds. I just leave them in the mold, decoration and all, till they're dry
enough to pop out and hold their form. So I'm thinking today's work will be
mixing glazes to use on the stuff currently in the kiln, and making more
plaster molds.
I must be nuts, I LOVE getting back to work. I WILL solve this...
Best--
Kate, still pushing that rock uphill....
| |
|
