Janet H Walker on wed 7 apr 99
I've been looking at a lot of books lately reading about making molds.
(Yeah, I'm not afraid to admit this. And there's a lot more to it than
meets the eye. And when I get the hang of it, I'll be happy to explain
to customers how the pieces are made. Anyhow, moving right along...)
Right at the moment, I'm interested in press molded pieces (not
tiles but plates and bowls). All of the examples shown use hump
molds, where the slab goes face down on the mold and you refine the
bottom while the thing sets up.
What about the other way around? The slump mold, where you would coax
the slab down into the mold and get to see the inside instead?
I would have thought that the slump mold was more "forgiving", in the
sense that the piece could shrink all it wanted wihtout getting stressed
the way it would if left on a hump mold unmonitored. Not so? I wondered
whehter there was some unwritten piece of moldy folk wisdom that says
"hump molds are the ones that work" or whether it is something else.
For example, the face of the piece goes against the mold and therefore
it will be more perfect compared to the lumpy thumbprinted face of
something that was forced into a slump mold.
Prob'ly this is an area where the pre-college teachers have more
experience than many of us. Any thoughts about what the advantages are
to slump molds vs hump molds?
Thanks,
Jan
Dwiggins, Sandra (NCI) on thu 8 apr 99
Janet--
I've tried putting a slab of clay into a deep concave mold. Not alot of fun.
You have to cut and dart the clay, just like fitting a piece of fabric. It is a
bit less problematic for a plate with a less concave profile. Try it. You
will immediately see the problems encountered in press molding concave forms.
You don't have to make a plaster mold to see this---just take any bowl--metal,
glass, even a bisque clay bowl will do, press in a clay slab.
I, too, think that the drying problems would be lessened doing it this way. I
do make my shallow plates this way and some small bowls.
I bought 2 books on mold-making at NCECA---glad I did!
Sandy
-----Original Message-----
From: Janet H Walker [SMTP:jwalker@world.std.com]
Sent: Wednesday, April 07, 1999 11:06 AM
To: CLAYART@LSV.UKY.EDU
Subject: slumping or humping?
----------------------------Original message----------------------------
I've been looking at a lot of books lately reading about making molds.
(Yeah, I'm not afraid to admit this. And there's a lot more to it than
meets the eye. And when I get the hang of it, I'll be happy to explain
to customers how the pieces are made. Anyhow, moving right along...)
Right at the moment, I'm interested in press molded pieces (not
tiles but plates and bowls). All of the examples shown use hump
molds, where the slab goes face down on the mold and you refine the
bottom while the thing sets up.
What about the other way around? The slump mold, where you would coax
the slab down into the mold and get to see the inside instead?
I would have thought that the slump mold was more "forgiving", in the
sense that the piece could shrink all it wanted wihtout getting stressed
the way it would if left on a hump mold unmonitored. Not so? I wondered
whehter there was some unwritten piece of moldy folk wisdom that says
"hump molds are the ones that work" or whether it is something else.
For example, the face of the piece goes against the mold and therefore
it will be more perfect compared to the lumpy thumbprinted face of
something that was forced into a slump mold.
Prob'ly this is an area where the pre-college teachers have more
experience than many of us. Any thoughts about what the advantages are
to slump molds vs hump molds?
Thanks,
Jan
Anne Hunt on thu 8 apr 99
Hi Janet--I've always enjoyed your posts, for both your forthrightness and
clay knowledge--new person that I am.
I'd been told by the Wise Heads that hump molds are ok, but you do run
the risk of cracking if you don't pull them off in time---in fact, it's
happened to me when i've done a bird-bathey thing humped over a large bowl.
Not a show-stopper, tho', and is manageable.
Have also found that some large slumped pieces can warp a tad as the
sides pulled away from the inside of the form; maybe 'cause they dried too
fast---also manageable.
Six of one, 1/2 dozen of the other. Luck!
anne & the cats
Dannon Rhudy on thu 8 apr 99
At 11:05 AM 4/7/99 EDT, you wrote:
>
interested in press molded pieces (not
>tiles but plates and bowls). All of the examples shown use hump
>molds, where the slab goes face down on the mold and you refine the
>bottom while the thing sets up.....
If you want slump molds and can't find them, you can throw your own
and then bisque fire them. Throw them fairly thick so that they'll be
sturdy once fired. If it were me, I'd incise a foot-ring in the bottom, so
that when I turned out my bowl the foot would already be on it. If you
do this, be sure to keep a rounded profile for the foot to ease removal
from the mold. AND while you're at it you can incise a ring at the top of
the mold if you want a nice full rounded rim on your bowl. Don't make
undercuts, or your clay will not come out, or at least it will not come out
easily. Just make some small ones to try. You might like them, might
not. When you make the bowls, if you line the mold with lightweight
paper towels you can make piece after piece without having to wait
for it to release. It will come right out if you invert it onto a bat for
drying.
New towel, new clay, next bowl,etc. I presume that one could do plates the
same way, but they are so quick to throw that it might not be worth it. But
give it a try, let us know.
Regards,
Dannon Rhudy
potter@koyote.com
>
>What about the other way around? The slump mold, where you would coax
>the slab down into the mold and get to see the inside instead?
>
>I would have thought that the slump mold was more "forgiving", in the
>sense that the piece could shrink all it wanted wihtout getting stressed
>the way it would if left on a hump mold unmonitored. Not so? I wondered
>whehter there was some unwritten piece of moldy folk wisdom that says
>"hump molds are the ones that work" or whether it is something else.
>For example, the face of the piece goes against the mold and therefore
>it will be more perfect compared to the lumpy thumbprinted face of
>something that was forced into a slump mold.
>
>Prob'ly this is an area where the pre-college teachers have more
>experience than many of us. Any thoughts about what the advantages are
>to slump molds vs hump molds?
>
>Thanks,
>Jan
>
Talbott on thu 8 apr 99
>----------------------------Original message----------------------------
>I've been looking at a lot of books lately reading about making molds.
>(Yeah, I'm not afraid to admit this. And there's a lot more to it than
>meets the eye. And when I get the hang of it, I'll be happy to explain
>to customers how the pieces are made. Anyhow, moving right along...)
>
mold making can be complicated, but I think there are a few things that can
simplify it:
- use good plaster. I've used some that was old or perhaps not
sotred well that didn't set, or some that set, then broke easily.
- use the right proportion of water to plaster. some of the books
have this information, but if you have ever bought a slump/hump mold, they
include the ratio. what i've done is carefully weigh the water, then mark
the container (something see through) and do the same with the plaster.
Then the next time you can use these two containers to measure your plaster
and water - only make sure you mix in a separate container.
- I've been tempted to sift the plaster into the water instead of
just putting it in with my hands.
- also if you have a drill with a mixter bit you could use that to
mix your plaster.
>Right at the moment, I'm interested in press molded pieces (not
>tiles but plates and bowls). All of the examples shown use hump
>molds, where the slab goes face down on the mold and you refine the
>bottom while the thing sets up.
>
I've made both hump and slump, and use the hump much more than the slump.
I make plates, plattes, and bowls this way. I don't throw a foot rim on
any. I do add a hand built foot rim for the platter to lift it off the
surface.
The reason why I prefer the hump is that I like to press texture into my
clay through the slab roller and then drap it over the hump. The inside
comes out nice and smooth.
>What about the other way around? The slump mold, where you would coax
>the slab down into the mold and get to see the inside instead?
>
slump might be better for some pieces, and may not warp as much. It does
take a little longer to make the piece and the inside won't be as smooth.
>I would have thought that the slump mold was more "forgiving", in the
>sense that the piece could shrink all it wanted wihtout getting stressed
>the way it would if left on a hump mold unmonitored. Not so? I wondered
>whehter there was some unwritten piece of moldy folk wisdom that says
>"hump molds are the ones that work" or whether it is something else.
>For example, the face of the piece goes against the mold and therefore
>it will be more perfect compared to the lumpy thumbprinted face of
>something that was forced into a slump mold.
>
I don't leave the clay on the hump molds very long - usually only ten or
fifteen minutes. then when I flip it, to avoid the sides from drooping, I
do this:
- put the hump mold with clay on your banding wheel.
- loosen the edges carefully with a tool.
- place a flat board or bat over the bottom of your piece.
- put some weight over that (kiln brick)
- take some strips of fabric and loosly go around the piece
- secure it with tape.
- flip your piece over so that it is now right side up
- set it aside to dry for a while, then remove the fabric
- when the piece is dry enough to hold it's weight, flip it
over so the bottom can dry. (I don't flip my platters - just
let them dry slow.)
>Prob'ly this is an area where the pre-college teachers have more
>experience than many of us. Any thoughts about what the advantages are
>to slump molds vs hump molds?
>
>Thanks,
>Jan
I hope this is helpful.
Celia
http://www.PotteryInfo.com
&
http://www.HuntAmerica.com
Marshall & Celia Talbott
P.O. Box 4116,
Naples, Maine 04055-4116
(207) 693-6100
e-mail: clupus@ime.net
---------------------------------------------------------------------
Vince Pitelka on thu 8 apr 99
>What about the other way around? The slump mold, where you would coax
>the slab down into the mold and get to see the inside instead?
Jan -
Steve Robison and Kathy Guss taught me a wonderful slump-mold method which
is now a standard part of my colored clay workshops. We make slump molds
out of rigid foam insulation board. With the thin stuff, cut it with a mat
knife. With the thick stuff, cut it with a sabre saw with an adjustable
foot, so you can set the blade at the angle you want. Draw the shape you
want on the top, leave enough level area on top for any level flange you
want, and cut the outer shape of the mold and the inner shape of the hole.
You do not really need for the angle of the inside cut to be exactly what
you want to end up with in your slumped pieces. Simply drape you slab
across the mold, and gently drop the mold against the table a few times
until the slab sags to the desired curvature. And of course you can coax
the slab into place with your fingers if you wish. If you wish, you can use
a deep mold and slump the slab to an even curvature, and add a coil foot
when the vessel is leather hard. Or, you can use a shallow mold so that the
slab slumps down against the table or board beneath, creating a flat surface
at the bottom.
I have never had any problem with the slabs sticking to the foam board.
They seem to release easily, even if I leave the piece on the mold until it
is dry. Of course, I roll out my slabs between layers of 10 oz. canvas
duck, and put them directly onto the slump molds with absolutely no moisture
on the surface, and the canvas texture no doubt helps keep the slabs from
sticking to the foam.
Good luck -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Carol Jackaway on fri 9 apr 99
I have been making alot of work doing both slump and hump. I have found, for
me, that if you are doing a large concave bowl, it is better the slump it.
The reason being that during the set up to leather hard, the walls are
supported and there is no cracking. Yes you do have to "dart" the clay and
push it alittle, but a couple passes with a metal rib on the interior takes
care of this. Once at the leather hard state pop it out add SMALL amount of
clay to areas not filled in by the "darting" process. To add a foot, score,
alittle clay slip and attach the foot. A shallow bowl, plates and platters
can all be hump molded and poped off right as the leather hard stage starts.
That gives you alittle freedom to reshape if you want. Hope some of this
helps.
Carol Jackaway
Delaware County Pa. where the sun is shining and the clay is calling
Bob & Ginny Bivaletz on fri 9 apr 99
hi folks, new subscriber here. i've been playing around with different
methods of slumping and humping and was wondering if one incised an
impression for a foot or rim ring in the bisqued slump mold and then pressed
your slab into it, would it not leave an indentation on the inside of the
bowl? thanks from ginny
-----Original Message-----
From: Dannon Rhudy
To: CLAYART@LSV.UKY.EDU
Date: Thursday, April 08, 1999 4:46 AM
Subject: Re: slumping or humping?
----------------------------Original message----------------------------
At 11:05 AM 4/7/99 EDT, you wrote:
>
interested in press molded pieces (not
>tiles but plates and bowls). All of the examples shown use hump
>molds, where the slab goes face down on the mold and you refine the
>bottom while the thing sets up.....
If you want slump molds and can't find them, you can throw your own
and then bisque fire them. Throw them fairly thick so that they'll be
sturdy once fired. If it were me, I'd incise a foot-ring in the bottom, so
that when I turned out my bowl the foot would already be on it. If you
do this, be sure to keep a rounded profile for the foot to ease removal
from the mold. AND while you're at it you can incise a ring at the top of
the mold if you want a nice full rounded rim on your bowl. Don't make
undercuts, or your clay will not come out, or at least it will not come out
easily. Just make some small ones to try. You might like them, might
not. When you make the bowls, if you line the mold with lightweight
paper towels you can make piece after piece without having to wait
for it to release. It will come right out if you invert it onto a bat for
drying.
New towel, new clay, next bowl,etc. I presume that one could do plates the
same way, but they are so quick to throw that it might not be worth it. But
give it a try, let us know.
Regards,
Dannon Rhudy
potter@koyote.com
>
>What about the other way around? The slump mold, where you would coax
>the slab down into the mold and get to see the inside instead?
>
>I would have thought that the slump mold was more "forgiving", in the
>sense that the piece could shrink all it wanted wihtout getting stressed
>the way it would if left on a hump mold unmonitored. Not so? I wondered
>whehter there was some unwritten piece of moldy folk wisdom that says
>"hump molds are the ones that work" or whether it is something else.
>For example, the face of the piece goes against the mold and therefore
>it will be more perfect compared to the lumpy thumbprinted face of
>something that was forced into a slump mold.
>
>Prob'ly this is an area where the pre-college teachers have more
>experience than many of us. Any thoughts about what the advantages are
>to slump molds vs hump molds?
>
>Thanks,
>Jan
>
Robert Wilt on fri 9 apr 99
Hi Jan,
Here are some wandering thoughts on hump and slump molds:
* Hump molds are probably more prevalent because they are easier to make.
For example, pour plaster into an old bowl. Making a plaster slump mold
is more work (you have to set up a box to contain the plaster).
Myself, I never liked working with plaster that much, so I make bisque
molds instead (I bisque them to make them sturdier, but they can be used
dry or LH). I make them by throwing, or by using slabs over some other
mold. Most of my bisqued bowl molds can be used on either side (and thus
are called "shlump" molds). Some of them have texture on one side.
To make molds for low odd-shaped flat-bottomed things, like square
plates or ovoid soap dishes or the like, I make a thick slab, mark and
cut the shape, and bevel the edges. Voila, a hump mold. It's not really
much harder to make a slump mold for the same shape: after you cut
the shape out of the slab, bevel the edges of the hole and sit the
remains on a piece of plasterboard (to act as the bottom of the mold).
Equivalently, you can roll or extrude a long fat coil, sit that on the
plasterboard, and use it as your mold. Some people in the studio use
beveled pieces of wood glued together in various shapes (sort of like
picture frames).
* Hump molds let you add a foot (or feet) right away. Slump molds hide
the foot from you until you take the clay out (at which point you may be
able to add feet, but not quite as easily).
* Hump molds are generally lighter for the same shape (especially if
made of plaster). It's the difference between the inside volume of the
shape, vs. the "outside" volume (a block of plaster minus the inside
volume).
* It's easier to mold the clay around the outside of a steeper shape on
a hump mold, than to fit the clay into a slump mold of the same shape.
On the other hand, the "lumpy thumbprinted" surface you mention
can be avoided if you use a moist sponge to work the clay down into
the mold.
* Hump molds (as you say) are less forgiving of drying shrinkage. Many of
my hump molds, though, let me take the piece off almost right away,
so shrinkage is not a problem. The ones that need to stay on the mold
the longest are the large shallow bowls. Steeper shapes, or shapes with
flat bottoms (plates, soap dishes, etc.) can usually come off in less
than an hour, sometimes right away, depending on thickness and the
softness of the clay. With hump-molded bowls, rather than add a foot
I sometimes take the bowl off the mold then sit it back on the mold
right-side-up to form a base.
* Slump molds let you work on the inside surface while the clay is still
soft - important for certain decorative techniques. Of course, to use
the same techniques on the outside, you need a hump mold. Some kinds of
decoration you can do to the slab before you put it onto the mold, but
you have to avoid smushing or smearing the decoration while fitting the
clay to the mold (unless that's part of the decoration).
* One of my favorite rim techniques, to fold the clay at the
edge back around the outside, works better on a hump mold. Another thing
I like to do is to pinch up the edge like a pie crust; that works better
with a slump mold.
* I usually cut my slabs before I put them onto (into) the mold, rather
than after. If you cut them before, you can round off both the inside
and outside edges of the rim with a damp sponge. It's harder to soften
the inside edge if you cut the slab on the hump mold (and vice versa for
slump molds). The disadvantage of pre-cutting is that it may require
precise placement of the slab on the mold (for centering or alignment,
if you need that). With smaller sizes, you can sometimes place the
mold upside-down onto the slab (easier to get precise placement),
then flip them over together.
There are some even more complicated considerations and ways to
make molds, much of which I learned from Lucy Scanlon. I'll try to get
her to write a book about it someday.
bob wilt
rjw@studiopotter.org
http://www.mdc.net/~rjwilt/
Bob Hanlin on fri 9 apr 99
Janet:
For years I've been making trays and platters by slumping them in various
trays and platters and trays that I've found, mostly in antique stores.
These work pretty well, but as they get deeper the results are less
acceptable. The clay is difficult to get into the form and since I use
quite a bit of texture on these it is usually spoiled in the effort. My
wife has been able to show me how to coax the clay down some. "It's like
getting pie crusts into a pan, silly."
Haven't tries the humps though....
>----------------------------Original message----------------------------
>I've been looking at a lot of books lately reading about making molds.
>(Yeah, I'm not afraid to admit this. And there's a lot more to it than
>meets the eye. And when I get the hang of it, I'll be happy to explain
>to customers how the pieces are made. Anyhow, moving right along...)
>
>Right at the moment, I'm interested in press molded pieces (not
>tiles but plates and bowls). All of the examples shown use hump
>molds, where the slab goes face down on the mold and you refine the
>bottom while the thing sets up.
>
>What about the other way around? The slump mold, where you would coax
>the slab down into the mold and get to see the inside instead?
>
>I would have thought that the slump mold was more "forgiving", in the
>sense that the piece could shrink all it wanted wihtout getting stressed
>the way it would if left on a hump mold unmonitored. Not so? I wondered
>whehter there was some unwritten piece of moldy folk wisdom that says
>"hump molds are the ones that work" or whether it is something else.
>For example, the face of the piece goes against the mold and therefore
>it will be more perfect compared to the lumpy thumbprinted face of
>something that was forced into a slump mold.
>
>Prob'ly this is an area where the pre-college teachers have more
>experience than many of us. Any thoughts about what the advantages are
>to slump molds vs hump molds?
>
>Thanks,
>Jan
>
>
Bob Hanlin
bhanlin@ionet.net
Oklahoma City, OK
Dannon Rhudy on sat 10 apr 99
----------
>hi folks, new subscriber here. i've been playing around with different
>methods of slumping and humping and was wondering if one incised an
>impression for a foot or rim ring in the bisqued slump mold and then pressed
>your slab into it, would it not leave an indentation on the inside of the
>bowl? thanks from ginny----------
Yes, indeed it does, Ginny. Make a clay coil, press it into the indentation,
and smooth it out when you smooth the rest of the interior of the bowl. Same
for rim.
.......>If you want slump molds and can't find them, you can throw your own
>and then bisque fire them. Throw them fairly thick so that they'll be
>sturdy once fired. If it were me, I'd incise a foot-ring in the bottom, so
>that when I turned out my bowl the foot would already be on it.......
Bonnie Staffel on mon 12 apr 99
April 10, 1999
Janet, to make deeper slump processes work, try cutting your circle
first, then cut the clay into the shape of butterfly wings, not quite
all the way through towards the base, but leave enough clay to cover the
base completely. Placing this into the deep mold you will find the
wings come together, probably overlap, then you can press the overlap to
make a seal. I made a pounder from a croquet ball with a glued on
wooden handle to beat the inside of the mold. To smoothe the inside
surface, you can then scrape the clay with a metal flexible rib. This is
hard to describe, but if you try it, you can then work with the shape of
the butterfly wing shapes so they come together to fit your mold. I
throw my own molds on the thick side and include a foot ring in the
bottom.
Bonnie Staffel bstaffel@freeway.net
>
Liz Willoughby on tue 13 apr 99
A nice little tool you can make when pressing the clay into a slump mold.
Take a baby cotton sock, fill it with sand, cut the ankle end off, sew
NEATLY, (guys take note), and use it to gently press the clay into the
mold.
>----------------------------Original message----------------------------
>April 10, 1999
>
>Janet, to make deeper slump processes work, try cutting your circle
>first, then cut the clay into the shape of butterfly wings, not quite
>all the way through towards the base, but leave enough clay to cover the
>base completely. Placing this into the deep mold you will find the
>wings come together, probably overlap, then you can press the overlap to
>make a seal. I made a pounder from a croquet ball with a glued on
>wooden handle to beat the inside of the mold. To smoothe the inside
>surface, you can then scrape the clay with a metal flexible rib. This is
>hard to describe, but if you try it, you can then work with the shape of
>the butterfly wing shapes so they come together to fit your mold. I
>throw my own molds on the thick side and include a foot ring in the
>bottom.
>
>Bonnie Staffel bstaffel@freeway.net
>>
Liz Willoughby
R.R.# 1
2903 Shelter Valley Rd.
Grafton, Ontario
Canada
e-mail, lizwill@phc.igs.net
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