JRodgers on fri 3 aug 12
With a good mold release agent, it should work. Normally, plaster molds
are used because they remove water to get the release. but it can be
done with other release agents. When I go this route, I will use most
any spray lube like Pam or a pro mold release like Polyease 2300,They
burn out when fired, but will interfere with any attachments.
John
On 8/3/2012 9:01 PM, pat gilmartin wrote:
> Does anyone have experience making press molds using Durham's Rock Hard, =
and if so, any advice on doing so? Release agents, etc.? I find that Plaste=
r of Paris to too soft to hold the impression well, and in the town where I=
live I cannot buy Casting Plaster, Mold Plaster, or any of the other stron=
ger plasters. I could order some, of course, but the delivery charges are p=
retty high. I'm thinking of trying Rock Hard.
>
pat gilmartin on fri 3 aug 12
Does anyone have experience making press molds using Durham's Rock Hard, an=
d if so, any advice on doing so? Release agents, etc.? I find that Plaster =
of Paris to too soft to hold the impression well, and in the town where I l=
ive I cannot buy Casting Plaster, Mold Plaster, or any of the other stronge=
r plasters. I could order some, of course, but the delivery charges are pre=
tty high. I'm thinking of trying Rock Hard.
Peggy Thompson on sat 4 aug 12
Press molds
On Aug 4, 2012 12:32 AM, "Peggy Thompson" wrote:
> Have you entertained the use of carved thick bisque clay as press molds?
> They work suite well and, depending on your climate, several pieces per d=
ay
> can result. Of course, the moisture level of the claybody will affect the
> number pulled and a balance between too wet but finer detail and dryer bu=
t
> not catching fine detail must be considered.Also the coarseness of either
> clay in mold and pressing will be evident in finished product.
>
> You fail to mention your plaster source however, too soft plaster that
> fails to set hard probably is too old and has absorbed moisture to degrad=
e
> results.Getting new plaster stored and shipped free of moisture needs an
> almost moisture proof airtight storage container.
>
> I, for example ,use a Rubbermaid trashcan with a high mill count inside
> double plastic bags closed on the newly purchased bag of plaster.
>
> I checked local business directory and under plaster and found molding
> plaster and check when the supply arrived and whether it is stored inside
> and request an inner located bag(s) , if possible.Pottery plaster is
> available at twice or so the price here, if you travel over 100 miles or
> pay extra shipping.
>
> Good luck
> Margaret in SC
> On Aug 3, 2012 11:44 PM, "pat gilmartin" wrote:
>
>> Does anyone have experience making press molds using Durham's Rock Hard,
>> and if so, any advice on doing so? Release agents, etc.? I find that
>> Plaster of Paris to too soft to hold the impression well, and in the tow=
n
>> where I live I cannot buy Casting Plaster, Mold Plaster, or any of the
>> other stronger plasters. I could order some, of course, but the delivery
>> charges are pretty high. I'm thinking of trying Rock Hard.
>>
>
Ric Swenson on sat 4 aug 12
No idea what Rock Hard is....gee...it sounds hard though...
but
tincture of green soap (available in your local drugstore) is a great plast=
er mold release agent...releasing plaster from plaster...Pam is oily and ha=
rd to get out of the pores IMHO. Green tincture of soap washes out easily. =
No release agent should be neccessary for releasing clay from plaster mold=
s....given a long enough casting time (thickness) and the proper clay body.
harder plasters, I believe, contain small amounts of cement....experimentat=
ion would make soft (plaster of Paris) plaster into ceramical or hydrocal =
type plaster...long lasting molds. Not so fast for casting, but harder long=
lasting molds that hold the detail for many castings.
my 2 cents.
ric
Ric Swenson, B.F.A, M.F.A.
Ceramist, Artist and Teacher.
Jing De Zhen Ceramic Institute
Jing De Zhen City,
Jiang Xi Province
China
Mobile: 86-13767818872
> Date: Fri, 3 Aug 2012 23:04:04 -0500
> From: jrodgers113@GMAIL.COM
> Subject: Re: making molds with Rock Hard
> To: Clayart@LSV.CERAMICS.ORG
>
> With a good mold release agent, it should work. Normally, plaster molds
> are used because they remove water to get the release. but it can be
> done with other release agents. When I go this route, I will use most
> any spray lube like Pam or a pro mold release like Polyease 2300,They
> burn out when fired, but will interfere with any attachments.
>
> John
>
> On 8/3/2012 9:01 PM, pat gilmartin wrote:
> > Does anyone have experience making press molds using Durham's Rock Hard=
, and if so, any advice on doing so? Release agents, etc.? I find that Plas=
ter of Paris to too soft to hold the impression well, and in the town where=
I live I cannot buy Casting Plaster, Mold Plaster, or any of the other str=
onger plasters. I could order some, of course, but the delivery charges are=
pretty high. I'm thinking of trying Rock Hard.
> >
James Freeman on sat 4 aug 12
On Fri, Aug 3, 2012 at 10:01 PM, pat gilmartin wrot=
e:
Does anyone have experience making press molds using Durham's Rock Hard,
and if so, any advice on doing so? Release agents, etc.? I find that
Plaster of Paris to too soft to hold the impression well, and in the town
where I live I cannot buy Casting Plaster, Mold Plaster, or any of the
other stronger plasters. I could order some, of course, but the delivery
charges are pretty high. I'm thinking of trying Rock Hard.
Pat...
You can certainly make a mold from Durham's water putty, but I don't think
it will work very well. It is not as absorbent as ordinary plaster because
of the plasticizing modifiers they mix in. For a press mold, it will
likely take significantly longer to release the clay than would ordinary
plaster. As they say, though, there is only one way to find out!
Molding plaster is the same thing as plaster of Paris. No difference. In
fact, all of the ordinary plasters are pretty much the same, the hardness
characteristics being largely determined by how finely it is milled or by
how it was cooked. The various modified plaster products, such as
Durham's, gypsum cement, Hydrocal, and the like all differ because of the
different modifiers they contain. Some ordinary plasters, such as Art
plaster and Casting plaster, contain surface hardening agents intended to
make painting easier, so these types will be less absorbent than pottery
plaster or plaster of Paris.
If you live near a larger city, there may well be a dental supply house.
They will carry dental plaster. It is essentially the same as plaster of
Paris or molding plaster in terms of hardness and absorbency, but sets much
more quickly.
You can increase the hardness of your plaster of Paris (or most any
plaster) by reducing the amount of water in your mix. The more water you
use, the softer the finished product. 70% water to plaster is a starting
point, not a hard and fast rule.
Plaster of Paris is certainly hard enough for a press mold. The problem
you are facing may well be only the normal deterioration of the mold. Each
time you use a plaster mold, a very thin layer of the surface dissolves
away. This is why plaster molds are considered "self-cleaning". Thus,
with each impression or cast, you will lose more and more of your detail.
You can usually get about 50 good impressions from a detailed mold (much
more from simple molds). If I will be using a press mold for a lot of
impressions, I will make a few clay impressions in the fresh mold, then
store that mold. I then pour production molds from the clay casts I made.
In this way, when the production molds become worn out, I still have the
very fresh original mold from which to take a few more impressions and make
new production molds.
Good luck with your project.
...James
James Freeman
"Talk sense to a fool, and he calls you foolish."
-Euripides
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources
JRodgers on sat 4 aug 12
James,
You are quite right about this. In my own practice, for molds with
intricate and delicate detail, I may use them as few as 15 times. For
simple molds with no detail, up to a hundred or so times. On all my
molds with intricate detail, I will make a rubber master mold for the
purposes of making more production molds, and from it the very first
mold is always set aside to preserve the detail. For molds that are of
lesser detail or no detail, I usually make a master mold of Ultracal 30,
and then save the first mold from it. That way, if I ever have to make
new molds, I use the masters. When the masters wear out, then I have a
clean detailed mold from which to make a new master. Redundancy is nice
in this business.
John
On 8/4/2012 11:17 AM, James Freeman wrote:
> Plaster of Paris is certainly hard enough for a press mold. The problem
> you are facing may well be only the normal deterioration of the mold. Ea=
ch
> time you use a plaster mold, a very thin layer of the surface dissolves
> away. This is why plaster molds are considered "self-cleaning". Thus,
> with each impression or cast, you will lose more and more of your detail.
> You can usually get about 50 good impressions from a detailed mold (much
> more from simple molds). If I will be using a press mold for a lot of
> impressions, I will make a few clay impressions in the fresh mold, then
> store that mold. I then pour production molds from the clay casts I made=
.
> In this way, when the production molds become worn out, I still have the
> very fresh original mold from which to take a few more impressions and ma=
ke
> new production molds.
Don Goodrich on sun 5 aug 12
Yes, Rock Hard will work as a press mold material, but it tends not to re=
=3D
lease as=3D20
well as plasters. Make sure your angles are as forgiving as possible.
Because Hydro-Stone, which I prefer, has become increasingly difficult to=
=3D
find, I=3D20
experimented for a while with various mixtures. One that worked besides D=
=3D
urham's=3D20
Water Putty was plaster of paris mixed with 10 percent Sakrete cement pat=
=3D
cher=3D20
sieved through a 60-mesh screen. Although a little of the smoothness was =
=3D
lost, it=3D20
was noticeably harder, set quickly and released well.=3D20
I never found a really satisfactory home-made mixture, so bit the bullet =
=3D
and made=3D20
the hundred mile drive for a supply of Hydro-Stone. For the small scale a=
=3D
t which I=3D20
work, one bag will last a long time.=3D20
As Peggy mentioned, bisque clay press molds can work really well. Making =
=3D
them=3D20
can be challenging but their durability is great.
Good luck with your quest,
Don Goodrich
http://dongoodrichpottery.com/
Julie Brooks on tue 7 aug 12
Hi All,
Laguna Clay Company carries Hydrocal and supplies to any Laguna
distributor who orders it.
Thanks,
Julie Brooks, Creative Director
Laguna Clay Company
800-452-4862 ext 211
| |
|
