nikom chimnok on sun 21 mar 99
Hello slipcasters,
I'm sure you're familiar with this problem: After slipcasting a
piece, you can see the mold lines. You scrape them off, wash them off, and
they're gone. Then you fire the piece and they magically reappear.
I've read many times the reason for this problem: particle
orientation. I remember diagrams and discussions, showing how the particles
line up flat against the sides of the mold, and also flat on the sides of
the miniature crack between pieces of the mold. But what I don't rememer is
how you prevent this behavior.
What is the answer?
TIA
Nikom
In Northeastern Thailand, where it's hitting 100 F. every day now.
Jonathan Kaplan on sun 21 mar 99
>----------------------------Original message----------------------------
>Hello slipcasters,
> I'm sure you're familiar with this problem: After slipcasting a
>piece, you can see the mold lines. You scrape them off, wash them off, and
>they're gone. Then you fire the piece and they magically reappear.
> I've read many times the reason for this problem: particle
>orientation. I remember diagrams and discussions, showing how the particles
>line up flat against the sides of the mold, and also flat on the sides of
>the miniature crack between pieces of the mold. But what I don't rememer is
>how you prevent this behavior.
> What is the answer?
>TIA
>Nikom
>In Northeastern Thailand, where it's hitting 100 F. every day now.
Here's the trick.
Vertical seams will always show due to the reasons you cited above.
The soluciton is to design the ware so that the seams are somehow
contained, hidden, included, etc. etc. in the design of the wares. It
works.
Most mugs are jiggered rather than cast, or pressed, in both cases, the
seams are at the top rim.
Jonathan Kaplan, president
Ceramic Design Group LTD/Production Services
PO Box 775112
Steamboat Springs CO 80477
plant location
1280 13th Street Unit 13
Steamboat Springs CO 80487
(970) 879-9139 voice and fax
jonathan@csn.net
http://www.sni.net/ceramicdesign/
Jeff Lawrence on mon 22 mar 99
Nikom in Thailand wrote:
>Hello slipcasters,
> I'm sure you're familiar with this problem: After slipcasting a
>piece, you can see the mold lines. You scrape them off, wash them off, and
>they're gone. Then you fire the piece and they magically reappear.
> I've read many times the reason for this problem: particle
>orientation. I remember diagrams and discussions, showing how the particles
>line up flat against the sides of the mold, and also flat on the sides of
>the miniature crack between pieces of the mold. But what I don't rememer is
>how you prevent this behavior.
> What is the answer?
Hi Nikom,
What I do is actually compress the clay on the seams. My pieces have the
seam at a point where the clay changes direction, so we can just run a
rigid metal tool along the edge, compressing the clay and in theory
changing the particle orientation. Whether this theory is true, I don't
know. But the seams don't reappear.
You don't say what kind of pieces you are making, so I'm not sure this
would work for you.
Best regards,
Jeff
Jeff Lawrence
jml@sundagger.com
Sun Dagger Design
Rt. 1 Box 394L
Espanola, NM 87532
vox/fax 505-753-5913
Brian Crocker on mon 22 mar 99
Nikom,
Re; the joint lines,, this could be that your mould is old or you have slip on
the joining faces of the mould, I have found that you have to keep the faces
very clean, it is some times hard to see the little white pieces on the surface,
they can also be in the [ Natch ] location recesses.
If there is nothing holding your mould appart then I would re fit the two
parts together, that is place some carbon paper all over the surface of one
side of the mould, place the mould together and give it a few thumps with
your fist or preferrably with a rubber hammer, separate the mould and then
"very lightly"
scratch off the carbon paper marks {it is called 'bedding the mould'}
replace the carbon paper and thump it again, and again scratch off the marks.
When you have about 80% mark around the inner edge of the mould at the joint
line it is time to stop and cast a part to check.
However before you start to 'bed the mould' check the edge of the mould at
the joint line, that is where the new part touches, if it is not sharp but
rounded your mould is 'old' and all your work to re-bed it will be of no
use. Then it is time to throw the mould away and make a new one. If you cast
your own moulds use
"Plastic Natches" {mould locators}.
You can get them from Harrison & Meyor [I am not sure about the spelling] or
the Royal Society for the Blind in South Australia make them. Send your
address and I will get a sample for you.
Hope this helps,
keep in touch.
Kind regards Brian.
At 06:01 PM2:10: 21/03/99 EST, you wrote:
>----------------------------Original message----------------------------
>Hello slipcasters,
> I'm sure you're familiar with this problem: After slipcasting a
>piece, you can see the mold lines. You scrape them off, wash them off, and
>they're gone. Then you fire the piece and they magically reappear.
> I've read many times the reason for this problem: particle
>orientation. I remember diagrams and discussions, showing how the particles
>line up flat against the sides of the mold, and also flat on the sides of
>the miniature crack between pieces of the mold. But what I don't rememer is
>how you prevent this behavior.
> What is the answer?
>TIA
>Nikom
>In Northeastern Thailand, where it's hitting 100 F. every day now.
>
>
Brian Crocker
4 Erica Street,
Tea Tree Gully 5091,
South Australia,
Australia. {e.mail} crocker@dove.com.au
" When a Potter Gives or Sells Pots. Part of a Life is Given Also " CR
OC.
Reid Harvey on mon 22 mar 99
Dear Nikom Chimnok and Clayartists,
To answer the question as to the best way of preventing mold lines may
first require an understanding as to the reasons for doing this. Can you
tell us more about these reasons? After all, most of the time the mold
lines are covered by glaze, and the fact is that it is not always easy
to find an answer.
Here in Cote d'Ivoire I do a lot of mold casting and don't have the same
problem. The reason for this is that my claybody is hard to
deflocculate, so does not have the same tendencies in particle
orientation. (This, of course, does lead to altogether different
problems, such as a difficulty in maintaining uniform wall thickness.)
It might sound like a strange solution to the problem, but maybe you
could use materials that do not have such a pronounced tendency to the
classic models of particle orientation.
Other answers might be to change the mold design, so that the lines are
not visible. For example, many people who are new at slipcasting would
make the mistake of making a mug mold in two pieces, for the two sides
of the mug. This would leave an unsightly mold line straight across the
bottom of the mug. Instead these molds should be three pieces, with the
third, altogether separate piece for the footing.
But again, if you could give more detail as to why you do not want to
see the mold lines, perhaps other answers could be found. Quite often
ceramic design necessitates looking at every step of the process.
Reid Harvey
----------------------------Original message----------------------------
Hello slipcasters,
I'm sure you're familiar with this problem: After slipcasting a
piece, you can see the mold lines. You scrape them off, wash them off,
and
they're gone. Then you fire the piece and they magically reappear.
I've read many times the reason for this problem: particle
orientation. I remember diagrams and discussions, showing how the
particles
line up flat against the sides of the mold, and also flat on the sides
of
the miniature crack between pieces of the mold. But what I don't rememer
is
how you prevent this behavior.
What is the answer?
Louis Katz on tue 23 mar 99
If you have a bad problem with mold lines it is probably the result of too
much plastic material in your slip. This answer was pulled from memory of
written material not experiece.
Louis
nikom chimnok wrote:
> ----------------------------Original message----------------------------
> Hello slipcasters,
> I'm sure you're familiar with this problem: After slipcasting a
> piece, you can see the mold lines. You scrape them off, wash them off, and
> they're gone. Then you fire the piece and they magically reappear.
> I've read many times the reason for this problem: particle
> orientation. I remember diagrams and discussions, showing how the particles
> line up flat against the sides of the mold, and also flat on the sides of
> the miniature crack between pieces of the mold. But what I don't rememer is
> how you prevent this behavior.
> What is the answer?
> TIA
> Nikom
> In Northeastern Thailand, where it's hitting 100 F. every day now.
--
Louis Katz
lkatz@falcon.tamucc.edu
NCECA Director At Large
Texas A&M-CC Division of Visual and Performing Arts Webmaster (512) 994-5987
Visit the NCECA World Ceramics Image Database
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