Eleanora Eden on sun 19 mar 06
Hi Jim and all,
A mold for slip-casting a bowl is a one-piece mold.
The slip casting forms when a skin develops as the plaster mold takes
moisture from the slip. The thickness of the casting is a function of how
much time the slip is left in the mold.
If you have never made a mold here is the way I do it. I do a lot of mold
making in ceramics with a pretty easy and unique method. It is always successful.
1. Judge volume of pour (if you keep a log of your pours it will help).
2. Volume of plaster desired = volume of dry plaster. Only FRESH #1
pottery plaster should be used. Know your source. Ask how long the bags
have been around. Keep opened bag wrapped tightly in plastic.
3. Volume of water = 2/3 volume of dry plaster.
So. Measure your water and pour it in a container large enough. Dump
plaster in and mix for afew minutes. When it's thickened like cream it's
ready. When it's thickened like pudding it's more than ready. 5 minutes
is usually max mixing time.
Whenever possible I use leather-hard (or softer) clay positives.
This makes removing the positive a breeze. (It doesn't necessarily wreck
the positive. I can usually make as many molds from one positive as I want.)
We just took a bunch of pictures of the way I finish a casting in the mold
on the wheel so the piece will have the same lovely rim (and general "look")
as a thrown piece.
I'll get that set of photos completed as that pot goes through the process
and will post them on my webpage and announce it here. I'll make sure
to have a photo of the empty mold included.
Eleanora
>I have been doing thrown and hand built work but have not tried slip casting.
>I want to make duplicates of a soup bowl with cone 6 slip and need advice on
>making a mold.
>The question is: do I make a one piece mold that just does the outside form
>of the bowl, or two piece, forming inside / outside, with a pour hole.
>Would a two piece have problems with air entrapment?
>
>All advice welcome.
>
> Thank you, Jim May
>
>______________________________________________________________________________
>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.
James F. May Sr. on sun 19 mar 06
Hello Eleanora, thank you for your method. It sounds real good.
I am not clear on the proportions, is that two parts water to three
parts plaster?
What is the web site address that you spoke of?
Thanks again , Jim
Eleanora Eden wrote:
>Hi Jim and all,
>
>A mold for slip-casting a bowl is a one-piece mold.
>
>The slip casting forms when a skin develops as the plaster mold takes
>moisture from the slip. The thickness of the casting is a function of how
>much time the slip is left in the mold.
>
>If you have never made a mold here is the way I do it. I do a lot of mold
>making in ceramics with a pretty easy and unique method. It is always successful.
>
>1. Judge volume of pour (if you keep a log of your pours it will help).
>
>2. Volume of plaster desired = volume of dry plaster. Only FRESH #1
>pottery plaster should be used. Know your source. Ask how long the bags
>have been around. Keep opened bag wrapped tightly in plastic.
>
>3. Volume of water = 2/3 volume of dry plaster.
>
>So. Measure your water and pour it in a container large enough. Dump
>plaster in and mix for afew minutes. When it's thickened like cream it's
>ready. When it's thickened like pudding it's more than ready. 5 minutes
>is usually max mixing time.
>
>Whenever possible I use leather-hard (or softer) clay positives.
>This makes removing the positive a breeze. (It doesn't necessarily wreck
>the positive. I can usually make as many molds from one positive as I want.)
>
>We just took a bunch of pictures of the way I finish a casting in the mold
>on the wheel so the piece will have the same lovely rim (and general "look")
>as a thrown piece.
>
>I'll get that set of photos completed as that pot goes through the process
>and will post them on my webpage and announce it here. I'll make sure
>to have a photo of the empty mold included.
>
>Eleanora
>
>
>
>
>
>
>>I have been doing thrown and hand built work but have not tried slip casting.
>>I want to make duplicates of a soup bowl with cone 6 slip and need advice on
>>making a mold.
>>The question is: do I make a one piece mold that just does the outside form
>>of the bowl, or two piece, forming inside / outside, with a pour hole.
>>Would a two piece have problems with air entrapment?
>>
>>All advice welcome.
>>
>> Thank you, Jim May
>>
>>______________________________________________________________________________
>>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.
>>
>>
>
>
>
>
>
James F. May Sr. on sun 30 apr 06
Hello Eleanora, thank you for your wonderful advise.
I started casting in my first bowl mold, last week.
I started at thirty minutes and although a little heavy, it was probably
good for learning handling
and finishing, which really went well on the wheel.
Today, I will pour my second mold, for another style of bowl.
I thank you again for excellent advise and clear photography on your site.
Jim May
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