Plaster Mold For Casting Dinner Plates

[natanata]

Hello everyone!

Another question from me:

is it possible to cast a flat plate (without a foot) with a one-piece plaster mold?

I am usually throwing a prototype with a simple white clay on a wheel, then wait until its dry enough and cast a mold,
but when i tried making a plaster mold for a flat plate, plaster seemed to heavy for the clay to hold, clay got softer and caved in. As the result: the mold is with a little knob in the middle.

Any advices?
Thank you!
Nata

 

[Evelyne Schoenmann]

 Hi natanata. Why don't you bisque fire the prototype first, before casting a mold?

 

Evelyne

[PeterH]

I'm a little confused about a one-piece mould for a plate (assuming that you're casting rather than draping/pressing the plate).

 

FYI this rather nice little book describes how to make a 2-piece mould for a plate with foot-ring.

http://www.bookfinder.com/search/?ac=sl&st=sl&ref=bf_s2_a1_t1_1&qi=6db1GZqtsK2HL0feYKuQljdIRK8_1441707622_1:501:3311&bq=author%3Dsasha%2520wardell%26title%3Dslipcasting

... as you can see 2nd-hand copies can be quite cheap.

[Repeat the search using your preferred shipping destination and currency.]

 

PS You can look-inside the book at amazon

http://www.amazon.co.uk/Slipcasting-Ceramics-Handbooks-Sasha-Wardell/dp/0713676728/ref=sr_1_1?s=books&ie=UTF8&qid=1441708723&sr=1-1&keywords=slipcasting

[Denice]

I was making myself a set of dishes and I wasn't good enough at throwing to get my plates to nest well together or be the same size.  I made a hump mold that had pins in it that fit my wheel head.  I would put a slab of clay on it and kind of throw it into the mold and put a foot on the plate.  Plates came out great.  Denice

[PeterH]

Thanks, good idea. Sort of hand-jiggering.

http://pottery.about.com/od/potteryglossarygj/g/jiggers.htm

[Judith B]

If you use a mould, I would not slipcast it, but rather roll a slab of clay and press it gently inside the mould. As for making the mould, just like Evelyne said, bisquing the prototype should work better. Remember to make it bigger and also, to use soap on the piece before you pour the plaster!

[Pres]

Years ago a local artist threw these really large platters. Redware with slip decoration. Every one was oooh and aaahh over his throwing skills as these were 24-36" in size. So I went to a State teachers conference and he was demonstrating on the wheel. He started out rolling out a really large slab, took it over to a plaster form on the wheel laid the slab on the form, let if slump into the form and then started pulling the clay on the form to take the shape, and force clay into the foot ring base, working the clay back and forth. He said that he like to leave some of the finger marks in the clay, would let it set up for a few hours and flip it.  Impressive ?!??! but then who am I to judge?

[Leila]

On 9/9/2015 at 12:48 AM, Pres said:

would let it set up for a few hours and flip i

Yes, impressive, and we come back to the "flipping big moulds" discussion lately.

Did he flip with the board with two wheels you mentioned before?

On 9/9/2015 at 12:48 AM, Pres said:

pulling the clay on the form to take the shape,

Pres, please explain,  

If I understand, the slab was covering the inside of the mould,  how did he pull,  pressing from the centre  outward ? How did he work the clay back and forth?

 

[Pres]

The clay slab was laid into the plaster form. The plaster form had a foot ring groove in the bottom. The slab was laid into this, it was thicker than the finished form. He used a center to outward movement with his hands to move the clay outward and thin it while also forcing clay into the foot ring area. the slab was probably about 4 inches smaller in diameter than the finished plate, but by working from the center outward he mad up for that distance. If he wanted a smaller diameter he just cut it with a wooden tool so as not to damage the plaster or contaminate the form.

Flipping was done with a large round bat on top of the form and the whole thing flipped by two people.

 

best,

Pres