Vince Pitelka on tue 10 jun 08
Paul Borian wrote:
"I need to modify my clay body so it can dry very fast without cracking,
especially since I have a/c in the studio now and it will probably by
running all summer so the pots dry fast, plus I generally put them into
the bisque kilns when they are leather hard. I believe that many people
add sand to the clay body to help accomplish this - is that correct? Are
there disadvantages to using sand? I recall reading a long time ago that
it can cause dunting but I don't know to what extent."
Paul -
To me your thinking above seems backwards. You do not add sand to a
claybody so that you can dry it super fast. You add sand to give texture
and to improve working structure. It is true that it does open up the
claybody and it will be able to dry faster with less problems, but you
should not add sand unless you like working with a sandy claybody.
So, why do your pots dry too fast, and why do you put them in the bisque
kiln when they are leather hard? Why do you even bother to make pots if you
are going to subject them to that kind of risky drying and firing? What is
the point of that? Why not build some simple damp cabinets to dry the pots
slower, and why not wait until they are drier before firing them? Why are
you in such a hurry? Why not restructure your production schedule to allow a
more graceful drying process? You could still produce just as many pots,
but it will take more room for slower drying.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Paul Borian on wed 11 jun 08
Vince wrote:=20
"So, why do your pots dry too fast, and why do you put them in the
bisque
kiln when they are leather hard? Why do you even bother to make pots if
you
are going to subject them to that kind of risky drying and firing? What
is
the point of that? Why not build some simple damp cabinets to dry the
pots
slower, and why not wait until they are drier before firing them? Why
are
you in such a hurry? Why not restructure your production schedule to
allow a
more graceful drying process? You could still produce just as many
pots,
but it will take more room for slower drying."
=20
Well, first of all I probably should have mentioned that the cracks
started when I slightly increased the amount of foundry hill and
slightly decreased the amount of goldart in my clay body (which I did to
make it more refractory) and the cracks mostly showed up when I did the
final drying in the bisque kilns. I have been doing this for a year with
almost no problems at all, only until I made that small change. So now I
went back to the original formula but it got my thinking about how to
make the body a little more resistant to cracking, that's why I thought
about sand - especially since I have the a/c going most of the day which
dries things a lot faster.
=20
Now, as to why I push things so fast through the production system -
that is because I make my living entirely by wholesaling this pottery
and I simply have to move as fast as possible, and the fact that my clay
studio is pretty small means I just don't have room for a lot of wet
pots sitting around. So I have to get them out of the clay room (garage)
and into the electric kilns in the kiln shed to free up space so I can
make more. PLUS I throw all plates and platters on "hardybacker board"
which dries them really fast so the body has to be able to take that.
The fact that I have more work than I can deal with at this moment when
all indications are that this economy is basically going to grind to a
halt makes me want to push even harder while the demand for my pottery
is still there - because I know it is only a matter of time before
things slow down for me.
=20
BTW, Vince - weren't you the one who told me that you bisque all your
pots where you teach at the leather hard stage? That was one of the
things that got me started on it - and no problems until just recently.
=20
Thanks,
Paul
=20
Steve Slatin on wed 11 jun 08
Vince --
Perhaps I misread Paul's original query,
but I think that for sme of us it is
legitimate -- or even necessary -- to dry
things faster. A lack of space for slow
drying is one possible reason.
My studio -- 16 by 18 ft -- is more than
sufficient for the winter months, when
I experiment and have low output, but
when it's summer, and I have various
folks pushing me me to do sets of plates
and so on -- things that take lots of
drying space -- I want them to dry
quickly. If they don't, I have to
curtail my production to have enough
space for them to dry.
The slow dry I prefer -- a few days
under plastic, then a few days under
newspaper, then exposed to the air --
takes lots of space and time. In the
winter, it's fine, but in the summer
I don't need a damp cabinet to
encourage slower drying, I need a dry
cabinet to encourage faster drying.
I read Paul's question as 'how can
I safely get my ware dryer faster,
and will sand as a grog do it?' or
something similar. As per the above,
I believe it is a legitimate question,
and I'd be interested to see your
reply to that question.
Best wishes -- Steve Slatin
--- On Tue, 6/10/08, Vince Pitelka wrote:
> Paul Borian wrote:
> "I need to modify my clay body so it can dry very fast
> without cracking,
> especially since I have a/c in the studio now and it will
> probably by
> running all summer so the pots dry fast, plus I generally
> put them into
> the bisque kilns when they are leather hard. I believe that
> many people
> add sand to the clay body to help accomplish this - is that
> correct? Are
> there disadvantages to using sand? I recall reading a long
> time ago that
> it can cause dunting but I don't know to what
> extent."
>
> Paul -
> To me your thinking above seems backwards. You do not add
> sand to a
> claybody so that you can dry it super fast. You add sand
> to give texture
> and to improve working structure. It is true that it does
> open up the
> claybody and it will be able to dry faster with less
> problems, but you
> should not add sand unless you like working with a sandy
> claybody.
>
> So, why do your pots dry too fast, and why do you put them
> in the bisque
> kiln when they are leather hard? Why do you even bother to
> make pots if you
> are going to subject them to that kind of risky drying and
> firing? What is
> the point of that? Why not build some simple damp cabinets
> to dry the pots
> slower, and why not wait until they are drier before firing
> them? Why are
> you in such a hurry? Why not restructure your production
> schedule to allow a
> more graceful drying process? You could still produce just
> as many pots,
> but it will take more room for slower drying.
> - Vince
Mike on thu 12 jun 08
My biggest problem with sand/silica is that it doesn't melt, and leaves
rough/sharp spots on the surface of the pot. Found that feldspar sand
has the same effect as silica sand regarding cracking and drying, but
the feldspar sand melts partially in firing, rounding out its edges,
thereby leaving a smoother surface.
Mike
in Taku, Japan
www.karatsupots.com
karatsupots.etsy.com
karatsupots.blogspot.com
blogs.yahoo.co.jp/karatsupots
Ivor and Olive Lewis on fri 13 jun 08
It would seem that having a wide distribution of particle sizes and
geometric forms, spherical, cubic and foliate, is necessary . Such
variety might prevent stacking and bedding that would close capillary
pathways through which water can flow and water vapour diffuse.
About the value of Sand. which is classified as being 2.00 mm down to
0.0625 mm (62.5/1000 mm). Clay is from 4/1000 mm down. Material in the
gap
between is classed as "Silt"
Perhaps the governing factors that influence drying ability of a clay
and its green strength are vapour pressure, temperature, relative
humidity and barometric pressure of the local environment. Capillary
pathways or Openness" could be of minor significance. Only when
rapidly rising temperature creates steam would there be real problems.
Reassert relating to this topic was done at Alfred and is recorded by
W. E. Brownell in "Structural Clay Products". Ch 5 "Drying processes".
ISBN 3-211-81382-9.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Kim Hohlmayer on mon 16 jun 08
Hi Mike,
Where do you get feldspar sand? It sounds like something I would like to try. And what is the firing range? Thanks -- Kim H.
--- On Thu, 6/12/08, Mike <mike@KARATSUPOTS.COM> wrote:
From: Mike <mike@KARATSUPOTS.COM>
Subject: Re: Sand in a stoneware body - advantages, disadvantages?
To: CLAYART@LSV.CERAMICS.ORG
Date: Thursday, June 12, 2008, 9:06 AM
My biggest problem with sand/silica is that it doesn't melt, and leaves
rough/sharp spots on the surface of the pot. Found that feldspar sand
has the same effect as silica sand regarding cracking and drying, but
the feldspar sand melts partially in firing, rounding out its edges,
thereby leaving a smoother surface.
Mike
in Taku, Japan
www.karatsupots.com
karatsupots.etsy.com
karatsupots.blogspot.com
blogs.yahoo.co.jp/karatsupots
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