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hump mold thought, was re: slipware plates

updated sun 16 jan 05

 

Steve Irvine on thu 13 jan 05


Kate,

I actually use this technique on a regular basis to make textured bowls. There are two photos
of a double walled bowl on the second page of my website:
http://www.steveirvine.com/page2.html
I use a freshly made slab of clay and press it down on the bisque mould while it is turning on
the wheel. It stays on the mould for only about 5 minutes, then it is taken off and I let it dry
to leather hard, and then throw a pedestal type foot for it. It's an interesting way to get
texture on the inside of a bowl. Definately give it a try!

Steve Irvine
http://www.steveirvine.com

>Another similar technique involved laying your sheet of clay over a hump
>mold that had a design impressed into it,
>_Naturally_, I want to try this, too, when I can spare the clay to make a
>bisque mold (since that's what "they" used.) (Waiting for an order
>now...) In that case I'd think you'd need to put it over the mold while it
>was softer than leather-hard in order to pick up the design, pressing it
>gently over the mold, then being careful to remove the clay at the correct
>time to prevent cracking at is dries.
>
>Anyone tried this one?

Kate Johnson on thu 13 jan 05


WOW, Steve, that's gorgeous.

> I actually use this technique on a regular basis to make textured bowls.
> There are two photos
> of a double walled bowl on the second page of my website:
> http://www.steveirvine.com/page2.html
> I use a freshly made slab of clay and press it down on the bisque mould
> while it is turning on
> the wheel.

So the turning of the wheel helps to force the clay down into the
interstices of the mold and helps make sure it's evenly distributed?
(Applying logic when all else fails.)

It stays on the mould for only about 5 minutes, then it is taken off and I
let it dry
> to leather hard,

Is your mold plaster, so it wicks enough moisture away that the bowl is firm
enough not to distort? I'm always walking that fine line between unmolding
things too quickly and warping them, and having them get too dry...not a
problem in a slump mold, of course.

and then throw a pedestal type foot for it. It's an interesting way to get
> texture on the inside of a bowl. Definately give it a try!

Oh, I will! Just trying to figure out how to make a form I can carve,
now.

(Love the gold leaf on your bowl by the way...elegant, beautiful...)

Best--
Kate

Elizabeth Priddy on fri 14 jan 05


If you make a slump mold and a hump mold off of it, you can hump to form it and then pass it back into the slump to dry.

If the consistency is right and the shape, you can use large cheap plastic serving platters and bowls for this. just drape the bottom side of a form with thin muslin and form the hump molds form and then place the receiving form over it. Turn over and let it dry in the more friendly part.
This is with just the bowls.

You can also get a large bowl or platter form made of heavy plastic at a dollar store, make a plaster form for hump molding out of the plastic. Buy several plastic bowls. Form the piece over the plaster and then place the plastic receiving bowl over the muslin covered clay/plaster, turn the whole thing over, pull off the plaster and begin again. You can basicly make as many as you have plastic bowl space for the pieces to sit around in and dry. Take out of the plastic bowls and off to wire racks to dry once it is set up to stiff leather hard.

It works for me. It is a moderate studio production technique, saves plaster and space for storing molds as the mold and all the plastic bowls can sit together when not in use. So you can store a system for making about ten bowls at a time in the space of one plaster mold. You can make about 8-10 pieces a day off the same plaster in this way. For large platters and bowls for decorating, it should keep you in forms faster than you can fire them off.


Kate Johnson wrote:
I'm always walking that fine line between unmolding
things too quickly and warping them, and having them get too dry...not a
problem in a slump mold, of course.

Elizabeth Priddy

252-504-2622
1273 Hwy 101
Beaufort, NC 28516
http://www.elizabethpriddy.com
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Steve Irvine on fri 14 jan 05


>WOW, Steve, that's gorgeous.
>Is your mold plaster, so it wicks enough moisture away that the bowl is firm
>enough not to distort? I'm always walking that fine line between unmolding
>things too quickly and warping them, and having them get too dry...not a
>problem in a slump mold, of course.

Kate,

Thanks for the comments about my work.

I make my hump moulds out of bisque fired clay. I start by throwing a thicker than usual
bowl, not too deep, fairly wide. While it is still on the wheel, I throw a collar of clay inside the
bowl so that it is about an inch taller than the rim of the bowl. When the bowl/collar pot is
leather hard, I flip it over and trim a nice even surface on what would normally be the
underside of the bowl. Sitting on top of its collar, the whole thing now looks sort of like a
mushroom. At this point you can carve a pattern into the hump mould. After it has been
bisqued, I centre up the mould on the wheel (the extension of the collar below the rim makes
it easier to anchor the mould on the wheel with clay wads) and go through the making
process mentioned in the earlier post in this thread.

To get it off the mould I wait about 5 minutes and then gently hold the fresh clay part in my
hand and give a blow of air between the clay and the mould, the new clay bowl will just pop
off. I then pick up a wooden bat with my other hand, put it to the rim of the new bowl, flip it
over and voila! the new bowl is on a bat, no distortions, waiting to have its foot thrown on.

Hope this helps. The process is much easier than it sounds all written out like this!

Steve Irvine
http://www.steveirvine.com

Kate Johnson on fri 14 jan 05


Elizabeth, thank you!



> If you make a slump mold and a hump mold off of it, you can hump to form
> it and then pass it back into the slump to dry.

Do you have any advice about making a hump mold off the slump mold? as in
making sure you don't wreck the slump mold getting the hump out of it? I'm
taking about the plaster ones I just made, for instance...a layer of
cheesecloth between, or Murphy's, or???
>
> If the consistency is right and the shape, you can use large cheap plastic
> serving platters and bowls for this. just drape the bottom side of a form
> with thin muslin and form the hump molds form and then place the receiving
> form over it. Turn over and let it dry in the more friendly part.
> This is with just the bowls.

Makes sense...

>
> You can also get a large bowl or platter form made of heavy plastic at a
> dollar store, make a plaster form for hump molding out of the plastic.
> Buy several plastic bowls. Form the piece over the plaster and then place
> the plastic receiving bowl over the muslin covered clay/plaster, turn the
> whole thing over, pull off the plaster and begin again. You can basicly
> make as many as you have plastic bowl space for the pieces to sit around
> in and dry. Take out of the plastic bowls and off to wire racks to dry
> once it is set up to stiff leather hard.

Excellent, will do! This is wonderful advice...
>
> It works for me. It is a moderate studio production technique, saves
> plaster and space for storing molds as the mold and all the plastic bowls
> can sit together when not in use. So you can store a system for making
> about ten bowls at a time in the space of one plaster mold. You can make
> about 8-10 pieces a day off the same plaster in this way. For large
> platters and bowls for decorating, it should keep you in forms faster than
> you can fire them off.

Great, and thank you. Off to the dollar store to see if I can find more
good mold material. I found a very nicely shaped (18th c. style) soup bowl
and plate at Walmart, but they're glass/china (one each)...but haven't used
them for plaster mold making, yet. I've used them to mold clay in directly,
with Pam as a release, but I'd like to replace with plaster and move beyond
the Pam solution if possible. I've had much better luck with the plaster
stuff so far...

Best--
Kate

Kate Johnson on fri 14 jan 05


Hi Steve...

> Kate,
>
> Thanks for the comments about my work.

Well deserved...
>
> I make my hump moulds out of bisque fired clay. I start by throwing a
> thicker than usual
> bowl, not too deep, fairly wide. While it is still on the wheel, I throw a
> collar of clay inside the
> bowl so that it is about an inch taller than the rim of the bowl. When the
> bowl/collar pot is
> leather hard, I flip it over and trim a nice even surface on what would
> normally be the
> underside of the bowl. Sitting on top of its collar, the whole thing now
> looks sort of like a
> mushroom.

Got it. Makes sense...I'll need to build it or mold it, though, no
wheel....

At this point you can carve a pattern into the hump mould. After it has
been
> bisqued, I centre up the mould on the wheel (the extension of the collar
> below the rim makes
> it easier to anchor the mould on the wheel with clay wads) and go through
> the making
> process mentioned in the earlier post in this thread.

It would also make it easier to cut the edge neatly (sorry, Russel), with
a little rise there...
>
> To get it off the mould I wait about 5 minutes and then gently hold the
> fresh clay part in my
> hand and give a blow of air between the clay and the mould, the new clay
> bowl will just pop
> off.

Whoa! That's a new trick!

I then pick up a wooden bat with my other hand, put it to the rim of the
new bowl, flip it
> over and voila! the new bowl is on a bat, no distortions, waiting to have
> its foot thrown on.

So you put it rim down to dry, too, after doing the foot? (For the type of
stuff I'm doing, there's generally no foot, just a flat area on the bottom
of a bowl...)
>
> Hope this helps. The process is much easier than it sounds all written out
> like this!

Yes, makes sense, thank you!

Best--
Kate

Elizabeth Priddy on sat 15 jan 05


Regarding the regular bowl plaster parts: I don't like the cheescloth texture left on things. so I uuse muslin or flour sack material. The cloth you use can add a "feature" to the molded plate. I like it smooth because I am basicly just making bowl-shaped canvases to paint on. The material can be used with the plaster, the plaster will still wick moisture as long as the cloth is thin, like silk. That is how I keep it from sticking. The slip work you are doing might require some tweaking for this technique, but if the slip is truly melded to the clay, I don't see why it wouldn't still work. I do this with very wet slabs, but I think you would still have to wait for soft leather.

Regarding getting a hump mold out of an already made slump mold: Since I am using muslin between my plaster for easy removal, I am just basicly using the mold for form, not to wick moisture, making the plaster impermeable isn't a problem for me and so I use thick oil, like vegetable oil or vaseline... But here is a guess. I have never found that murphy's oil works to release things at a rate I like. try this test on some scrap plaster. Coat the surface of it with oil and put clay on it. You willl see that it slides and will not stick. Immediately wipe it all off, and then sand the surface lightly until you get to fresh plaster. If done consistently across the surface, and the oil was only on there for a short time, not long enough to soak in, you should be able to clean off a few millimeters and be back down to clean normally working plaster. Then put clay on the scrap and see if it works like the plaster did when you started. this would mean that it would work on a larger
mold as well. TO get the scrap, you could either make a few sacrifice pieces or just take an unsatisfactory piece you have and break it.

Rodgers, from the list is really the one who knows plaster, but he seems to be using it in the traditional manner for casting, so you would really need to comply with the Murphy's and other water soluble release materials. I really only use it for forming. Like if you make some jewelry shapes and place them in a pan, cover it in plaster, you then have a place to build colered clay and slip and composite clay jewelry.

None of my molds are from explicitly designed works, just the really plain basic shapes. For something inricate, I am not sure you want an exact duplicate anyway, so couldn't you press clay into the crevices and lightly coat the whole piece in clay. when your pour plaster in it, you should get a generic blank of the ornate form. and the clay will be sacrificed.



Kate Johnson wrote:

Elizabeth, thank you!



> If you make a slump mold and a hump mold off of it, you can hump to form
> it and then pass it back into the slump to dry.

Do you have any advice about making a hump mold off the slump mold?

...Great, and thank you. Off to the dollar store to see if I can find more
good mold material. I found a very nicely shaped (18th c. style) soup bowl
and plate at Walmart, but they're glass/china (one each)...but haven't used
them for plaster mold making, yet. I've used them to mold clay in directly,
with Pam as a release, but I'd like to replace with plaster and move beyond
the Pam solution if possible. I've had much better luck with the plaster
stuff so far...

Best--
Kate

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Elizabeth Priddy

252-504-2622
1273 Hwy 101
Beaufort, NC 28516
http://www.elizabethpriddy.com

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Laurie Cowell on sat 15 jan 05


>>Elizabeth, you wrote:

>>"You can also get a large bowl or platter form made of heavy plastic at a
>>dollar store, make a plaster form for hump molding out of the plastic.
>>Buy several plastic bowls. Form the piece over the plaster and then place
>>the plastic receiving bowl over the muslin covered clay/plaster, turn the
>>whole thing over, pull off the plaster and begin again. You can basicly
>>make as many as you have plastic bowl space for the pieces to sit around
>>in and dry. Take out of the plastic bowls and off to wire racks to dry
>>once it is set up to stiff leather hard."

Question: How does the plastic bowl receiving bowl fit over the clay
draped plaster mold? Doesn't the thickness of the clay make the bowl
larger than the plastic bowl?

Laurie Cowell

Carol Ross on sat 15 jan 05


>
Kate -
I used to make quite a few 2-part molds (and a few several part molds).
I like Murphy's oil between the two pieces (for you it would be slump
& hump) but it seems like I used to put something (newspaper? cloth?
thin metal?) just along the edges so that I'd have an easier time
getting the two parts separated... Elizabeth said she uses thin fabric
with the wet clay - I'm wondering if you couldn't just separate the two
sections with a tightly woven fabric - or plastic wrap! - since you
could re-work the surface of the finished hump to eliminate any marks
from the fabric?
Hope that helps... something else to think on while you wait for your
clay!
Carol R.
http://homepage.mac.com/portfolio.carolross/Menu4.html


> ...Great, and thank you. Off to the dollar store to see if I can find
> more
> good mold material. I found a very nicely shaped (18th c. style) soup
> bowl
> and plate at Walmart, but they're glass/china (one each)...but haven't
> used
> them for plaster mold making, yet. I've used them to mold clay in
> directly,
> with Pam as a release, but I'd like to replace with plaster and move
> beyond
> the Pam solution if possible. I've had much better luck with the
> plaster
> stuff so far...
>
> Best--
> Kate
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
>
> Elizabeth Priddy
>
> 252-504-2622
> 1273 Hwy 101
> Beaufort, NC 28516
> http://www.elizabethpriddy.com
>
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>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
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> melpots@pclink.com.
>

Elizabeth Priddy on sat 15 jan 05


as long as the slab is less than a half an ich thick and consistent, it is not a problem with an open form like a wide bowl or platter. Shapes that are near vertical walled or very deep do not work with this method. But high walled forms don't need wall support as much with soft slab techniques.

Laurie Cowell wrote:>>Elizabeth, you wrote:

>>"You can also get a large bowl or platter form made of heavy plastic at a
>>dollar store, make a plaster form for hump molding out of the plastic.
>>Buy several plastic bowls. Form the piece over the plaster and then place
>>the plastic receiving bowl over the muslin covered clay/plaster, turn the
>>whole thing over, pull off the plaster and begin again. You can basicly
>>make as many as you have plastic bowl space for the pieces to sit around
>>in and dry. Take out of the plastic bowls and off to wire racks to dry
>>once it is set up to stiff leather hard."

Question: How does the plastic bowl receiving bowl fit over the clay
draped plaster mold? Doesn't the thickness of the clay make the bowl
larger than the plastic bowl?

Laurie Cowell

______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org

You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/

Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.



Elizabeth Priddy

252-504-2622
1273 Hwy 101
Beaufort, NC 28516
http://www.elizabethpriddy.com

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