Dannon Rhudy on sat 30 aug 97
I have had a student from the jewelry fabrication/repair department
ask me how he could make a crucible, for a one-time bronze cast.
What he essentially wants to know is 1) what ceramic material(s)
are used to make a crucible (he called some companies that make
crucibles and of course they did not tell him); and 2) does it have
to be the ususal bowl-shape to work. Apparently he wants to use
it in some way in a centrifuge, in the process of making something
for a project. Since the shape he wants is specific to the
project, he cannot (he says) buy one; so wants to make it himself.
I have no specific information regarding crucibles, and hesitate
to either ENcourage or DIScourage his efforts. I thought perhaps
someone on the list might have information that would be helpful
to him or me or both. Any input would be welcome; I'll then pass
it on to his instructor. And thanks. You can send direct to me,
or if you think it of general interest to the list, post to the
list.
Dannon Rhudy
potter@koyote.com
Karl P. Platt on sun 31 aug 97
It's not worth the fuss to make a crucible. Doing so is fairly involved
and requires a lot of care -- having the crucible spring a leak either in
the furnace or while handling it hot is at best a messy thing to have
happen and at worst very dangerous. Crucibles are cheap and readily
available from a variety of sources - give a call to Hagstotz in Phila,
Ipsen Ceramics, Pecatonica (I love that name), IL or for larger sizes
Laclede-Christy in St. Joseph, MO.
Larry Phillips on mon 1 sep 97
Dannon Rhudy wrote:
> I have no specific information regarding crucibles, and hesitate
> to either ENcourage or DIScourage his efforts. I thought perhaps
> someone on the list might have information that would be helpful
> to him or me or both.
Bronzes vary in their melting (and pouring) temperatures, but a search
on Yahoo showed me one at http://www.atlasmetal.com/a87610.htm
Its pouring point is no higher than 2150 deg. F. I would think that
a cone 10 crucible might stand the heat. Your mileage may vary.
BobWicks@aol.com on tue 2 sep 97
I have been making my own crucibles for centrafuged lost wax casting and have
never had a problem. For small crucibles it is no fuss at all. Obviously
for larger projects you would have other considerations. Here is what I use
and I have never had any cracking.
Crucible Body ^6
42 Plastic Fire Clay
08 Bentonite
20 Medium to fine grogg
15 Sand
15 Flint
MIX DRY soak in water for one week. 50% of total should be water.
Reference
Saunders , GLAZES FOR SPECIAL EFFECTS, PG 35
John H. Rodgers on sun 7 sep 97
-- [ From: John H. Rodgers * EMC.Ver #2.5.02 ] --
-------- REPLY, Original message follows --------
Dannon, by all means I would suggest that you encourage your student. What
he really wants is a casting mold for lost wax casting and the centrifugal
casting process, used widely in jewelry manufacture.
In my own experience using centrifugal casting two types of vessels are
used. One is the vessel or crucible in which the metal is melted. This is
usually a very highfire porcelain ( for gold and silver at least). They have
different shapes according to their application but are mainly sized and
shaped for kind and amount of material to be melted. . Second is the Casting
Mold, and this is what I think your student wants.This is made from a high
temperature material called investment plaster (available through Kerr, Rio
Grande, Inc. and others). Investment plaster is cast over a wax model. Once
set the casting is placed in a steamer to melt out the wax. It is then
placed in an oven to burn out any residual wax or contaminants and to bring
the temperature up to approximately 1750F to receive the molten casting
metal.
When the metal ( bronze, silver, gold etc) is melted and at the right
temperature, the centrifugal force of the casting machine forces the molten
metal out of the crucible and into the hot mold. Though very hot, there is
always a significant temperature difference between the mold and the metal
in the crucible even though the mold is hot out of the oven. This prevents
thermal shock and shattering of the mold. When the molten metal hits the hot
mold it will solidify almost instantly. After sitting for a few minutes the
hot mold is plunged into a bucket of cold water. This will cause the
investment plaster to explode under water, freeing up the casting inside.
Once free(and cool) the casting can be cleaned up, bead blasted, buffed,
polished, and a patina applied.
As can be seen from the description of this process, the investment mold is
always destroyed, so a new one must be made for each new casting. The trick
is to be very careful and clean, chase, and re-detail that first casting and
make a vulcanized rubber mold of the original casting. This allows one to
make many wax reproductions which can be invested, and then cast in metal.
Or, as your student says he wishes to do, make only one. In my own
experience, I always found it to be a good idea to make a rubber mold for
posterity, just in case you ever needed to do it again.They keep a very long
time.
Have your student check out Romanoff at http://www.ROMANOFF.com
Rio Grande, Inc. at http://www.
riogrande.com/
Hopes this helps.
John Rodgers
Date: Saturday, 30-Aug-97 09:37 AM
From: Dannon Rhudy \ Internet: (potter@koyote.com)
To: CLAYART LIST \ Internet: (clayart@lsv.uky.edu)
Subject: crucibles
----------------------------Original message----------------------------
I have had a student from the jewelry fabrication/repair department ask me
how he could make a crucible, for a one-time bronze cast. What he
essentially wants to know is 1) what ceramic material(s) are used to make a
crucible (he called some companies that make crucibles and of course they
did not tell him); and 2) does it have to be the ususal bowl-shape to work.
Apparently he wants to use it in some way in a centrifuge, in the process of
making something for a project. Since the shape he wants is specific to the
project, he cannot (he says) buy one; so wants to make it himself.
I have no specific information regarding crucibles, and hesitate to either
ENcourage or DIScourage his efforts. I thought perhaps someone on the list
might have information that would be helpful to him or me or both. Any
input would be welcome; I'll then pass it on to his instructor. And thanks.
You can send direct to me, or if you think it of general interest to the
list, post to the list.
Dannon Rhudy
potter@koyote.com
-------- REPLY, End of original message --------
WHC228@AOL.COM on tue 13 aug 02
Anyone;
Do you know anything about the makeup of ceramic crucibles that could be used
in a glass furnace. I made a bunch of them for a friend that lives near me
and they all seem to want to crack.
I do not know the makeup for firebrick and for kiln shelves, but I suspect
that the materials are similar.
I am about to try a raku body that Standard Ceramics sells that has a lot of
kyanite in it.
We have been using a mixture of molochite, ball clay, grog, and fireclay. I
have tried using them in the color furnace that he fires, both bisked and
fired to cone 10. The cone 10 crucibles crack right away.
If you know anyone that has tried this and made it happen I would like to
talk to him/her.
Many thanks
Bill Campbell
Arnold Howard on tue 13 aug 02
I don't know the formula for making crucibles. Commercially made
crucibles are very expensive. You might want to ask this question
on www.warmglass.com.
Arnold Howard
Paragon
--- WHC228@AOL.COM wrote:
> Anyone;
> Do you know anything about the makeup of ceramic crucibles that
> could be used
> in a glass furnace. I made a bunch of them for a friend that
> lives near me
> and they all seem to want to crack.
> I do not know the makeup for firebrick and for kiln shelves, but
> I suspect
> that the materials are similar.
> I am about to try a raku body that Standard Ceramics sells that
> has a lot of
> kyanite in it.
> We have been using a mixture of molochite, ball clay, grog, and
> fireclay. I
> have tried using them in the color furnace that he fires, both
> bisked and
> fired to cone 10. The cone 10 crucibles crack right away.
> If you know anyone that has tried this and made it happen I would
> like to
> talk to him/her.
> Many thanks
> Bill Campbell
>
>
______________________________________________________________________________
> 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.
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billy on tue 13 aug 02
The book Contemporary Ceramic Formulas by John Conrad lists several
formulas for crucibles.Here are a couple:
R121 Crucible Body
Georgia kaolin 40
Calcined kaolin 20
Tenn ball clay 20
Fine grog 10
Flint 10
Temp ^9
shrinkage 14%
R124 Crucible Body
Plastic fireclay 50
Fine grog 30
Calcined kaolin 20
Temp ^9
shrinkage 14%
If you are doing much of this sort of stuff you ought to get yourself a
copy of this book. It is a good reference to have around.
Billy
Paul Herman on tue 13 aug 02
Bill,
I don't know any formulas, but I noticed that Laguna Clay sells "dry
crucible body" in 50 lb bags. Anyone used this stuff?
Hardway Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
----------
>From: WHC228@AOL.COM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Crucibles
>Date: Tue, Aug 13, 2002, 11:17 AM
>
> Anyone;
> Do you know anything about the makeup of ceramic crucibles that could be used
> in a glass furnace.
Ditmar on tue 13 aug 02
Any basic formula should give a satisfactory crucible.
Problems are usually in how they're used...or abused as the case may be.
Just as you wouldn't put a cold pot into a hot kiln, a crucible needs to =
be charged and brought up to temperature slowly too. Same for cooling. =
...slowly.=20
The larger the crucible, the slower and more carefully it needs to be =
fired up.
Get more information on proper crucible use. I'll bet that's where the =
problem is.
D
Michael C Hill on wed 14 aug 02
I posted a formula for crucibles on clayart a few months back. Its a
great formula, have used it for many years. The shape, thickness, and
fireing are all very important.
Give me a call if you want to talk about it
Michael
605-267-2116
----- Original Message -----
From: WHC228@AOL.COM
Date: Tuesday, August 13, 2002 1:17 pm
Subject: Crucibles
> Anyone;
> Do you know anything about the makeup of ceramic crucibles that
> could be used
> in a glass furnace. I made a bunch of them for a friend that lives
> near me
> and they all seem to want to crack.
> I do not know the makeup for firebrick and for kiln shelves, but I
> suspectthat the materials are similar.
> I am about to try a raku body that Standard Ceramics sells that
> has a lot of
> kyanite in it.
> We have been using a mixture of molochite, ball clay, grog, and
> fireclay. I
> have tried using them in the color furnace that he fires, both
> bisked and
> fired to cone 10. The cone 10 crucibles crack right away.
> If you know anyone that has tried this and made it happen I would
> like to
> talk to him/her.
> Many thanks
> Bill Campbell
>
>
________________________________________________________________________
______
> 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.
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