plaster-msg - 3/17/99
Use of plaster in period. References. How to use.
NOTE: See also the files: casting-msg, frescoes-msg, painting-msg, tiles-art, pottery-msg, block-printing-msg, masks-msg.
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From: ALBAN at delphi.COM
Newsgroups: rec.org.sca
Subject: Plaster of Paris
Date: 13 Mar 1998 22:58:17 -0500
Constance De LaRose said
>I learned that the most common ceramic form material used is
>plaster of paris. Guess what, plaster of paris is out of period so
>it was back to the research to learn that they used porous
>earthenware molds.
Not that I would ever suggest that someone not do research on
better materials for mold making, but, um, er, Constance? Plaster
of Paris _does_ seem to be period:
General reference: The Encyclopaedia Britannica, 15th ed. (1981),
vol. VIII, p. 30: "Used since ancient times, plaster of paris is so-
called because gypsum was early used near Paris to make plaster
and cement."
Specific reference: Cennino Cennini (in his _Il_ _Libro_
_dell'Arte_, trans. by Daniel V. Thompson, jr., New York;
Dover Publications, Inc., 1960. ISBN 486-20054-X; the original's a
mid-fifteenth century Italian work) uses Plaster of Paris for the
making of molds from life. "Have the man or the woman
stretched out; and have him put these little tubes into the
nostrils of his nose, and have him hold them himself, with his
hand. Have some plaster of Paris ready, made and roasted, fresh
and well sifted. Have some tepid water near you in a basin, and
put some of this plaster briskly on top of this water. Work
swiftly, for it sets fast; and do not get it either too liquid or not
enough so. Take a glass: take some of this preparation, and put it
on, and fill in around the face with it."
Of course, whether it was used for Constance's purpose in
period, I do not know - but at least the stuff itself is period.
(And for those of you wanting to cast from life with PoP, don't. It
gets hot to the touch, ver
y hot; I once measured a batch with a
thermometer, and it topped at 125 degrees Fahrenheit. There are
other ways of life casting. . . )
Alban, whose database of shtuff amazes even him. . .
Date: Tue, 2 Feb 1999 16:27:53 -0700
From: "J. A. Smith" <jasmith at caverns.com>
To: <sca-arts at raven.cc.ukans.edu>
Subject: Re: Plaster on Wood?
From: Rikki Mitman <esmitman at ghg.net>
>Has anyone made a plaster cast of a wooden object to use as a mold? Would
>the plaster stick to the porous wood as badly as I suspect?
>
>Teleri ferch Pawl
A friend of mine suggests using vaseline, much like you do when you make
casts of people.
Lady Renna of Battersea, Caer Mithin Halle, Outlands
Date: Wed, 3 Feb 1999 02:24:47 -0600
From: Roberta R Comstock <froggestow at juno.com>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster on Wood?
On Tue, 02 Feb 1999 17:13:53 -0600 Rikki Mitman <esmitman at ghg.net>
writes:
>Has anyone made a plaster cast of a wooden object to use as a mold?
>Would the plaster stick to the porous wood as badly as I suspect?
>
>Teleri ferch Pawl
I haven't tried it, but would probably want to put somethingon the wood
to keep the plaster from sticking. Or maybe try making a clay impression
of the wooden object and then a plaster cast from the clay?
hertha
Date: Wed, 03 Feb 1999 11:56:49 -0800
From: Lady Eleanor <hekav at gte.net>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster on Wood?
A lot of art supply stores and craft stores carry mold making
materials. There is a material...which I can not remember the name of
at the moment..., but I believe there are several brand names on the
market, that is rubbery and flexible when set. It peels right of the
positive that you are casting, and is specifically made for molds that
have heavy undercuts, and such. If you wish, I will see if I can find
the name for you. I think this might cause you a great deal less
aggravation than starting right from plaster, which is brittle, heavy,
and very well might stick to a number of places on your original even
with careful application of vaseline or some other release material.
After you have your rubber-ish mold, then you would cast your plaster
copy in that.
I hope this is of some help.
Eleanor, Lady Leycestershyre
Date: Wed, 03 Feb 1999 12:45:30 -0800
From: Lady Eleanor <hekav at gte.net>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster on Wood?
I can't find my art supplies catalogs at the moment...(arrrgggh!)...but,
here is one product that I've heard works well...never used it myself.
It's called Instamold...mixes with water and sets in 2 minutes. Here's
a web page that carries it. I'll see if I can find more for you.
http://www.activa-products.com/molding.htm
Eleanor
Date: Wed, 03 Feb 1999 13:13:05 -0800
From: Lady Eleanor <hekav at gte.net>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster on Wood?
Further source info...
Check this site...
Go to the "Catalog" button (the yellow crayon, at the bottom of the
screen). Then go to #16 Clays, Casting, Sculpture and, Molding
Supplies. This will download a .PDF file for you (380K, I think).
Some of the products you want to look at are, Pliatex Mold Rubber,
Moulage (good for face casting), and Silicone RTV Mold Making Rubber.
Also, you might want to look at this link for a huge variety of art
supply houses. You might find other products or better prices at some
others. I get Texas' catalogs frequently...but haven't placed an order
yet, so don't know how their customer service may be. I'd check several
sources before you decide. :-)
http://www.handilinks.com/cat1/a/a150.htm
Lady Eleanor
Date: Wed, 3 Feb 1999 15:50:05 -0800 (PST)
From: sion warwick <lostboy_sion at yahoo.com>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster on Wood?
Another consideration is RTV (room temperature vulcanizing) rubber.
Its usually available at commercial plastic suppliers. I use GTE's
RTV11, which may be difficult to get (gives off dangerous fumes and is
supposed to only be available to contractors - just tell them you are
a contractor and use a little bravado and they should sell it to you -
works for me). There are also other versions available. You just
need to make sure they are rated to ~700 degrees or so for pewter. It
is a two part mixture like epoxy. Just make sure that it is in a well
ventilated area while curing. It takes about 24 hours to harden and
about 1 week to completely cure. I've found that when it is heated
during the casting process it gives off some fumes, so I always have a
fan going.
Here's a quick way to make a mold of an object: build a frame using
legos thats about twice the size of the object and put it on a board.
Put a layer of clay in the bottom of the frame and sink the object
halfway into the clay. Build a sprue with clay from one side of the
object to the lego frame. Mix RTV and fill the lego frame, making
sure the object is covered by at least 1/4 inch of rubber. Let cure
24 hours, then lift lego frame from board and remove clay, leaving
only enough to form the sprue. Slather it all in vaseline (the RTV
cures to itself really well!), then fill that side with RTV, again
making sure the object is covered by 1/4 inch rubber. Let cure 24
hours, then remove from frame and let cure 1 week. When casting with
the rubber mold, use something rigid (like masonite pieces) to
sandwich the mold when you are holding it, or it tends to gap and leak
hot metal. Also, I recommend pressing a small lego piece bumpy side
down into the clay before pouring the first RTV half to create
registration marks. Helps hold the mold together without it slipping.
Any other questions, feel free to contact me
Lady Sion
Date: Thu, 04 Feb 1999 15:44:48 -0700
From: Curtis & Mary <ladymari at cybertrails.com>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster of Paris may be period
plaster was molded and carved and used to decorate and elaborate the frames
for Altarpeices in the church. I believe also some secular works.
Mairi, ATenveldt
Date: Thu, 4 Feb 1999 22:11:15 -0500
From: "Helen Schultz" <meistern at netusa1.net>
To: <sca-arts at raven.cc.ukans.edu>
Subject: Re: Plaster of Paris may be period
Slaked plaster (a purified form of plaster of paris) was used to make one of
the gilding bases for Gold Leafing in manuscripts.
<proudly spoken like a long-time scribe :-)>
Katarina Helene
Date: Wed, 17 Feb 1999 03:04:26 EST
From: <EalasaidS at aol.com>
To: sca-arts at raven.cc.ukans.edu
Subject: Re: Plaster on Wood?
On Tue, 02 Feb 1999 17:13:53 -0600 Rikki Mitman <esmitman at ghg.net> writes:
>Has anyone made a plaster cast of a wooden object to use as a mold?
>Would the plaster stick to the porous wood as badly as I suspect?
>
>Teleri ferch Pawl
I'm running behind and someone may already have mentioned this, but in making
plaster casts of items for use with clay slip, we use "green soap" - it's
liquid soap and it stops the plaster from sticking to your original. You
should be able to get it at a good ceramic/pottery supply store.
As for someone's comment about being sure you can get the original out - build
yourself a wooden frame as deep as your mold needs to be, coat the sides and
bottom with green soap. Fill it half full and press your original object
halfway into the plaster. You will have to support it until the plaster dries
enough that it doesn't sink. After the plaster is totally hard, coat the
surface with green soap and fill the frame the rest of the way with plaster.
This gives you a mold that will easily split in half without destroying the
mold.
You didn't mention what you were going to use the mold for (or I missed it -
I"m speed reading...). If it's to pour something liquid (like slip), you need
to work a channel into the mold (I use a dowel, or make a clay plug that butts
up against the original). If your original has pokey out parts, you have to
plan carefully, otherwise you end up with a mold that won't open after
you've poured your casting material into it.
Ealasaid
<the end>