Kate Johnson on wed 12 jan 05
Hi Vince...
>
> Kate -
> I have only had success with thick-application slip techniques
> (feather-combing, marbling) on freshly thrown or rolled clay. Don't let
> the
> base clay dry at all. If you do, then the slip surface will crack upon
> drying or firing.
Siiiiigh...I thought that was what I should do, too, but my last two
attempts doing it that way have resulted in bit WET juicy cracks before the
slab base is anywhere near dry enough to move into a mold! Most
frustrating...
What surface to you work on? I'm suspecting that may be my problem. As I
said, I tried a layer of cheesecloth under this last slab (still on heavy
cardboard underneath) and got cracking again, long before I could move the
slab. I'm thinking a nice plaster bat might be the way to go...maybe a
sheet of wallboard, but with the paper on it, maybe not.
>
> The plate or slab has to be very well supported. In other words, you
> cannot
> apply thick slip for feather combing on the flange rim of a wet plate,
> because of course the extra introduced moisture will cause the flange rim
> to
> crack and collapse.
Yes, I think the problem is that my whole slab/surface gets too wet, then
doesn't work well on my drying surface.
>
> In doing feather-combing or marbling on slab work, I have always done it
> on
> freshly-rolled slabs, and then I have slumped or manipulated the slabs
> after
> the slip surface reaches the same consistency as the base clay.
My last two haven't gotten even CLOSE to that state before cracking...the
best luck I've had so far are the ones I've done in a plaster mold to begin
with. The next most successful ones have been those I made flat, then dried
with a hair dryer till they were leathery enough to move. The wet-wet
combination is fighting me...
There is a
> point where it is just a bit too soft and the slip decoration will smear,
> and a point where it is just a bit too hard, and it will crack when you
> try
> to bend the slabs. It can be very touchy.
I've noticed.
> Good luck -
Thank you! I think it takes good luck and excellent timing, too!
Best--
Kate
Meg Smeal on wed 12 jan 05
Re: Kate's travails with slipware -
The "old timers" actually did these plates a third way - slip trailing and feathering on the flat discs, letting them firm up and then flipping them upside down on a hump mold rather than in a bowl-like mold -
This has the added advantage of flattening out the design -
meg smeal
Kate Johnson on wed 12 jan 05
> Re: Kate's travails with slipware -
> The "old timers" actually did these plates a third way - slip trailing
> and feathering on the flat discs, letting them firm up and then flipping
> them upside down on a hump mold rather than in a bowl-like mold -
> This has the added advantage of flattening out the design -
Hi Meg! Yep, I saw that in one of my books...plan to try it in the near
future.
I'm guessing (not that I ever would have has such a stupid thing happen)
that you need to let the disc get leather hard or nearly so *before* adding
the slip decoration, in preparation for that step. (Last night I started
one with marbling before I went off to school, trying out the cheesecloth
under it to try to mitigate the tendency to make big old wet cracks. Er.
No....big old wet crack by the time I got home 3 hours later. That's twice
this has happened, the first time drying on cardboard, the second with
cheesecloth between.
So I utilized the usable part in a SMALL mold and cut the rest up into
little ovals and parallelograms and such for jewelry. )
You'd need to make sure the marbling or other design is fairly dry, I'd
think, before putting it face down on anything--it is SO delicate!
Have you tried this?
Best--
Kate
Vince Pitelka on wed 12 jan 05
> I'm guessing (not that I ever would have has such a stupid thing
> happen)
> that you need to let the disc get leather hard or nearly so *before*
> adding
> the slip decoration, in preparation for that step.
Kate -
I have only had success with thick-application slip techniques
(feather-combing, marbling) on freshly thrown or rolled clay. Don't let the
base clay dry at all. If you do, then the slip surface will crack upon
drying or firing.
The plate or slab has to be very well supported. In other words, you cannot
apply thick slip for feather combing on the flange rim of a wet plate,
because of course the extra introduced moisture will cause the flange rim to
crack and collapse.
In doing feather-combing or marbling on slab work, I have always done it on
freshly-rolled slabs, and then I have slumped or manipulated the slabs after
the slip surface reaches the same consistency as the base clay. There is a
point where it is just a bit too soft and the slip decoration will smear,
and a point where it is just a bit too hard, and it will crack when you try
to bend the slabs. It can be very touchy.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Vince Pitelka on thu 13 jan 05
> Siiiiigh...I thought that was what I should do, too, but my last two
> attempts doing it that way have resulted in bit WET juicy cracks before
> the
> slab base is anywhere near dry enough to move into a mold! Most
> frustrating...
Kate -
I just can't imagine this. I have never seen such cracks appear in a wet
slip-decorated slab, nor can I imagine any reason why they would occur,
other than a poorly supported slab. I mean, I believe you of course, but I
cannot figure out why it is happening.
When I do thick slip application on a slab, I just lay the slab on a plywood
wareboard, without anything under it. I like the fact that the board pulls
a little bit of moisture out of the slab. If you want some separation
medium, you could put a layer or two of newspaper under the slab. But the
point is that there shouldn't be any shrinkage going on at this stage, and
thus no reason for any cracking to occur.
I definitely would not put the slab on wallboard or plaster, because that
might remove too much moisture from the slab, and then when the slip layer
tried to catch up, it might crack.
The only other possiblilty here is that there is something strange going on
with your claybody. I have done thick slip applications on slabs rolled
from various stoneware and terracotta bodies, and never a problem like what
you describe.
The ONLY circumstances under which I can imagine such cracking is if the
slab is poorly supported, or if it is moved immediately on a medium that
flexes and stretches.
I hope this helps -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Kate Johnson on thu 13 jan 05
Hi Vince...
>> Siiiiigh...I thought that was what I should do, too, but my last two
>> attempts doing it that way have resulted in bit WET juicy cracks before
>> the
>> slab base is anywhere near dry enough to move into a mold! Most
>> frustrating...
>
> Kate -
> I just can't imagine this. I have never seen such cracks appear in a wet
> slip-decorated slab, nor can I imagine any reason why they would occur,
> other than a poorly supported slab. I mean, I believe you of course, but
> I
> cannot figure out why it is happening.
I'm still working on it myself. I was looking at the John Pollex book
Slipware today, though, and he shows a few troubleshooting photos. One of
them, pg. 74, has a big wet crack (at least that's what I'm assuming since
it's been my experience--maybe he's referring to the fact that it parallels
the edge of the plate), and says "This type of crack usually occurs when the
pot to be decorated has not dried sufficiently. I normally marble pots the
day after they are thrown." So....??
>
> When I do thick slip application on a slab, I just lay the slab on a
> plywood
> wareboard, without anything under it. I like the fact that the board
> pulls
> a little bit of moisture out of the slab. If you want some separation
> medium, you could put a layer or two of newspaper under the slab. But the
> point is that there shouldn't be any shrinkage going on at this stage, and
> thus no reason for any cracking to occur.
That would make sense to me, yes!
>
> I definitely would not put the slab on wallboard or plaster, because that
> might remove too much moisture from the slab, and then when the slip layer
> tried to catch up, it might crack.
>
Ah. Thank you, point taken...
> The only other possiblilty here is that there is something strange going
> on
> with your claybody. I have done thick slip applications on slabs rolled
> from various stoneware and terracotta bodies, and never a problem like
> what
> you describe.
If it happened all the time, I'd think so too, but it's the same stuff I've
been using, either Flint Hills red earthenware or Flint Hills terra cotta
(grogged). I think both of the recent problems have been after I ran out of
earthenware, but I've done others that didn't have a problem...
>
> The ONLY circumstances under which I can imagine such cracking is if the
> slab is poorly supported, or if it is moved immediately on a medium that
> flexes and stretches.
Ah ha. The heavy cardboard I had the slab on might have absorbed enough
water to warp a bit, I'll bet! Eureka, you may have solved it for me!
Trying hard to remember if the first time was on masonite or cardboard...
>
> I hope this helps -
Always! Thank you for your generosity...I will keep trying. Not for a bit,
though--I am now, however, officially Out Of Clay (except some year old buff
stoneware, which I'm eyeing wistfully--it's pretty stiff, but I'm
desperate!). The order's in but not sure when it will arrive...I made my
last mug today.
Just as well, probably...the three new molds I made Tuesday night are still
MUCH too damp to use, so I won't be as tempted...
Again, thank you--
Best--
Kate
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