Dennis Mummert on fri 26 jan 01
I have two problems to solve in the next couple of days. The first
one is a head scratcher. I've been using Columbus Clay stoneware
slip (c4-6), fired at cone 5 to produce a few products. Finally
found one that my customer was enthusiastic about, and she wants
more. I had previously done about 50 pieces out of this particular
mold with absolutely no problems. Cast great, fired good, glaze held
well with no pinholing. Now that the slip and the mold has been idle
for 4 months, I go back and start casting again. Mix the slip well
to make sure nothing settled, dump it in, dump it out, demold in
about 2 hours. Greenware dries well with no cracks. BUT, when I go
to fire it, it cracks a LOT. Sometimes the cracks follow the parting
line, but mostly they're random. They seem to start on the outside
of the piece. Most of them do not go all the way through. A few of
the pieces actually split in half, though. (not on the parting
line!) Took some pieces to Columbus Clay, along with some of the
slip and greenware. They had never seen the problem before. The
only thing we could figure was I might have gotten a bad batch of
slip and just coincidentally had the problem by grabbing the wrong
(bad) bottle.
Ok - second part. Columbus Clay gave me some porcelain slip to try
that has the same firing range. Same mold I've been using
successfully with the stoneware slip. It molds very fast - 10 or 15
minutes to achieve about 1/8" wall thickness. The piece is dry to
the touch in maybe another 15 minutes. Trouble is, it will NOT
release from the mold. I tried waiting an hour, then 4, then 12. I
have to tear the piece out every time.
I really need these pieces! They're Valentine's day oriented, and
the clock is ticking. I would welcome replies to my email address,
as I may miss them if posted here (at the bench trying to figure this
out!)
BTW, I typically MUST adjust the viscosity of commercial slip by
adding a tiny amount of sodium silicate and about 10 - 20 cc's of
Poly 211 per gallon. The Poly greatly improves the strength of the
greenware. Both water and sodium silicate need to be adjusted
minutely during an extended pouring operation due to evaporation and
CO2 reactions.
Jonathan Kaplan on fri 26 jan 01
on 1/26/01 12:08 PM, Dennis Mummert at dmummert@ERINET.COM wrote:
> Greenware dries well with no cracks. BUT, when I go
> to fire it, it cracks a LOT. Sometimes the cracks follow the parting
> line, but mostly they're random. They seem to start on the outside
> of the piece. Most of them do not go all the way through. A few of
> the pieces actually split in half, though. (not on the parting
> line!) Took some pieces to Columbus Clay, along with some of the
> slip and greenware. They had never seen the problem before. The
> only thing we could figure was I might have gotten a bad batch of
> slip and just coincidentally had the problem by grabbing the wrong
> (bad) bottle.
Sounds to me that you have garbage slip. The body is not compounded
correctly and or the defloculation is incorrect. Most of our business is
casting and I would be glad to help you but I will need more information on
the slip What is in it? What is the specific gravity? What is the viscosity?
How are you preparing you moplds to cast?
>
> Ok - second part. Columbus Clay gave me some porcelain slip to try
> that has the same firing range. Same mold I've been using
> successfully with the stoneware slip. It molds very fast - 10 or 15
> minutes to achieve about 1/8" wall thickness. The piece is dry to
> the touch in maybe another 15 minutes. Trouble is, it will NOT
> release from the mold. I tried waiting an hour, then 4, then 12. I
> have to tear the piece out every time.
Once again, garbage slip. Same as ablove applies. White colored casting
bodies should have some Velvacast clay in them which definitely creates a
VERY fast cast. THere are also some fast casting (FC-340 form Old Hickory)
ball clays that do this when the slip is improperly compounded by people who
really don't know also about casting body formulation, the necessry
deflocculation and visscosities.
>
> I really need these pieces! They're Valentine's day oriented, and
> the clock is ticking. I would welcome replies to my email address,
> as I may miss them if posted here (at the bench trying to figure this
> out!)
>
> BTW, I typically MUST adjust the viscosity of commercial slip by
> adding a tiny amount of sodium silicate and about 10 - 20 cc's of
> Poly 211 per gallon. The Poly greatly improves the strength of the
> greenware. Both water and sodium silicate need to be adjusted
> minutely during an extended pouring operation due to evaporation and
> CO2 reactions.
The above paragraph makes no sense to me. I have been casting for a long
long time and once again, it sounds like garbage slip.
Call me and I'll try and get you back to where you need to be with your slip
casting. Trust me, it is not rocket science nor should you be having these
problems.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
jdkaplan@cmn.net
Plant Location (use for all UPS, Common Carrier, and Courier deliveries)
1280 13th Street
Steamboat Springs CO 80487
Cindy Gatto on fri 26 jan 01
I have had this releasing problem in the past. What I did was use a releasing
powder that you coat the mold with before you pour into it. The one that I
found to work the best is from a supplier in Brooklyn called Jack D. Wolf. He
doesn't have a name for it it is his own recipe he calls magic dusting
powder.
Good Luck;
Mark
The Mudpit
228 Manhattan
Ave.
Brooklyn NY
11206
phone #
718-218-9424
E - Mail
Mudpitnyc@aol.com
www.Mudpitnyc.com
Jonathan Kaplan on fri 26 jan 01
on 1/26/01 1:39 PM, Cindy Gatto at Mudpitnyc@AOL.COM wrote:
> I have had this releasing problem in the past. What I did was use a releasing
> powder that you coat the mold with before you pour into it. The one that I
> found to work the best is from a supplier in Brooklyn called Jack D. Wolf. He
> doesn't have a name for it it is his own recipe he calls magic dusting
> powder.
> Good Luck;
> Mark
> The Mudpit
> 228 Manhattan
> Ave.
> Brooklyn NY
> 11206
> phone #
> 718-218-9424
> E - Mail
> Mudpitnyc@aol.com
> www.Mudpitnyc.com
>
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>
An old slip casters technique here. Its just talc. We use talk in an old
sock and if there are areas in a specific mold/piece that have release
problems, a light pounce (read LIGHT) of the sock will take care of it. It
is not meant to pounce the entire mold. If you need to do this, usually the
slip is at fault, more than likely. Sometimes molds are not made correctly,
and if this is the case, the consistency of the plaster mix (eg Pottery #1
at 70) is not correct and the absorbency of the mold thus is not correct.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
jdkaplan@cmn.net
Plant Location (use for all UPS, Common Carrier, and Courier deliveries)
1280 13th Street
Steamboat Springs CO 80487
WHC228@AOL.COM on sat 27 jan 01
Dennis
Your problem doesn't sound like it is the clay. You said that the molds had
been idle for a long time. That is probably where you problem lies. The mold
needs to have some water in it. The solution id simple. Take some clear water
and sponge it into the mold. Then you should cast it. The casting time will
probably be a little longer. When you demold the first cast do it again, To
see if you got your water right. It is a good idea to do this when using a
new mold if it is completely dry.
Bill Campbell
Jonathan Kaplan on sun 28 jan 01
It also appears that you may be experiencing problems with your slip in
terms of correct specific gravity and viscosity. It also could be formulated
incorrectly
Post me off the list or call me and I would be glad to help you with this
problem.
Best
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
jdkaplan@cmn.net
Plant Location (use for all UPS, Common Carrier, and Courier deliveries)
1280 13th Street
Steamboat Springs CO 80487
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