F.Melville on sat 31 mar 01
Karen Lookenott wrote:
>>Cindy,
It can be done on a normal medium speed glaze firing; however, your
customer should be told that the piece will craze eventually and that the
bisque is only soft fired.
Karen >>
If the glaze doesn't fit the pot, crazing may occur at some time, but if it=
=20
does fit, there is no reason for it to craze at any time. As for the=20
bisque being "only soft fired", please explain. I have been single-firing=
=20
for about 15 years and find my pots to be perfectly hard and durable.
Fran=E7oise Melville
http://indalopottery.tripod.com
Cherie Chadwick on sat 31 mar 01
In a message dated 3/31/2001 7:28:37 AM Pacific Standard Time,
fmelvill@RAPIDNET.NET writes:
> If the glaze doesn't fit the pot, crazing may occur at some time, but if it
>
Hi all,
I'm new to this group and hope to learn much from you all. :-)
Question: What is meant 'fitting' and 'glaze doesn't fit the pot'?
Regards, Cherie
Tommy Humphries on sat 31 mar 01
Hello cherie:
Just as the clay shrinks as it dries and is fired, so does the glaze. If the
glaze shrinks less than the pot, it can become compressed and shiver off the
pot as it cools, If the glaze shrinks more then it is under tension and will
craze. The ideal is to have the glaze under slight compression so that it
does not craze from heating and cooling.
A glaze that doesn't shiver or craze is said to fit the claybody.
This is a very simple explanation, but gets to the guts of the matter.
Tommy
----- Original Message -----
From: "Cherie Chadwick"
To:
Sent: Saturday, March 31, 2001 2:59 PM
Subject: Re: Single firings (question)
> In a message dated 3/31/2001 7:28:37 AM Pacific Standard Time,
> fmelvill@RAPIDNET.NET writes:
>
> Question: What is meant 'fitting' and 'glaze doesn't fit the pot'?
>
> Regards, Cherie
>
Wade Blocker on sun 1 apr 01
Cherie,
by glaze fit the following is meant : a glaze can crack, craze, fall off
the pot,perhaps even crack the pot. A crackle glaze can be decorative, but
is not advised for food safe surfaces.
Mia in ABQ
Paul Taylor on sun 1 apr 01
Dear Ababi
5% bentonite is the recommended amount. What you can get away with is the
real amount.
The big HOWEVER : Raw glazing unlike biscuit glazing depends how dry the
clay is when you put the glaze on. For instance a glaze that is mostly clay
you can glazes the pot when very wet; a glaze that depends on bentonite is
probably best glazed when the pot is nearly dry.
Sometimes - Glazing the pot wet (leather) hard you have distortion problems
and when it is dryer cracking problems and when the pot is completely dry
bubbling of the body. The cure for all those ills is to gaze half the pot
first - The inside or the outside first - and the other half when the pot
is as dry as when you first glazed it. The advantage of glazing the outside
first prevents handles cracking and bubbling which they tend to do if they
are completely dry . I expect you have trouble keeping pots damp and that
could complicate raw glazing so I think you may have trouble with uneven
drying that I do not have.
I liked your site and appreciate the good effort you put into teaching .
Is it very expensive to get a site completely to your self in Israel I
think you deserve one.
-- Regards from Paul Taylor
http://www.anu.ie/westportpottery
Those that live by rhetoric will lie by it
> From: Ababi
> Reply-To: Ababi
> Date: Sun, 1 Apr 2001 06:45:05 +0200
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Single firings (question)
>
> I read before that some bentonite must be added, I don't remember how much.
> I would like to know because I want to try a combination of two glazes,
> eventually will be crawling, but to save firing, I want the first glaze to
> apply as it was an engob on the greenware.
> Ababi Sharon
> ababisha@shoval.ardom.co.il
> http://members4.clubphoto.com/ababi306910/
>
Ababi on sun 1 apr 01
I read before that some bentonite must be added, I don't remember how much.
I would like to know because I want to try a combination of two glazes,
eventually will be crawling, but to save firing, I want the first glaze to
apply as it was an engob on the greenware.
Ababi Sharon
ababisha@shoval.ardom.co.il
http://members4.clubphoto.com/ababi306910/
----- Original Message -----
From: "Tommy Humphries"
To:
Sent: Sunday, April 01, 2001 4:15 AM
Subject: Re: Single firings (question)
> Hello cherie:
>
> Just as the clay shrinks as it dries and is fired, so does the glaze. If
the
> glaze shrinks less than the pot, it can become compressed and shiver off
the
> pot as it cools, If the glaze shrinks more then it is under tension and
will
> craze. The ideal is to have the glaze under slight compression so that it
> does not craze from heating and cooling.
>
> A glaze that doesn't shiver or craze is said to fit the claybody.
>
> This is a very simple explanation, but gets to the guts of the matter.
>
> Tommy
>
>
> ----- Original Message -----
> From: "Cherie Chadwick"
> To:
> Sent: Saturday, March 31, 2001 2:59 PM
> Subject: Re: Single firings (question)
>
>
> > In a message dated 3/31/2001 7:28:37 AM Pacific Standard Time,
> > fmelvill@RAPIDNET.NET writes:
> >
> > Question: What is meant 'fitting' and 'glaze doesn't fit the pot'?
> >
> > Regards, Cherie
> >
>
>
____________________________________________________________________________
__
> 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.
>
Ron Roy on fri 13 apr 01
This answer has two main problems.
The implication is - the glaze and clay when fired set up the problems that
can result in poor glaze fit.
In fact - at the end of the firing the clay and glaze fit perfectly -
because the glaze is not a solid. It adjusts to the body as the two cool -
until the glaze solidifies.
At that point the clay and glaze will contract at different rates and set
up stress between the two.
If the glaze contracts more than the clay it crazes. If the clay contracts
too much more than the glaze it will shiver off or break the pot.
When the clay contracts more than the glaze we say the glaze winds up under
compression - if enough compression the glaze will not craze - if too much
compression we will have dunting and/or shivering.
When we talk about shrinkage we mean what happens when clay dries and is
fired enough to at least partially melt it. Dry shrinkage and fired
shrinkage. These we call irreversible.
When we talk about the reversible expansion and contraction that fired clay
and glazes go through when heated and cooled we do not call it shrinkage -
we call it expansion for short but we really mean expansion when heated and
contraction when cooled.
If we reheat the clay and glaze until the glaze melts again the glaze will
adjust to the clay again - but the same factors that were there will appear
again when the glaze solidifies on cooling.
RR
>Just as the clay shrinks as it dries and is fired, so does the glaze. If the
>glaze shrinks less than the pot, it can become compressed and shiver off the
>pot as it cools, If the glaze shrinks more then it is under tension and will
>craze. The ideal is to have the glaze under slight compression so that it
>does not craze from heating and cooling.
>
>A glaze that doesn't shiver or craze is said to fit the claybody.
>
>This is a very simple explanation, but gets to the guts of the matter.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
ferenc jakab on sat 14 apr 01
> >
> >A glaze that doesn't shiver or craze is said to fit the claybody.
> >
> >This is a very simple explanation, but gets to the guts of the matter.
>
> Ron Roy
Ron Roy, as usual gives very useful answers. and his post on shrinkage etc.
made this process very clear. I want to add a little comment here for those
contemplating single firing, it is important to add a clay component to most
glazes used in the above process because glazes without clay do not shrink
as much as the green or re-wetted body being glazed and then tend to flake
off as the body dries and shrinks.
Feri.
Linda Blossom on sat 14 apr 01
> Ron Roy, as usual gives very useful answers. and his post on shrinkage
etc.
> made this process very clear. I want to add a little comment here for
those
> contemplating single firing, it is important to add a clay component to
most
> glazes used in the above process because glazes without clay do not shrink
> as much as the green or re-wetted body being glazed and then tend to flake
> off as the body dries and shrinks.
> Feri.
Actually, I have never found this to be true. I add veegum (a binder) to
all my glazes and sieve them and have never had a problem. I am talking
about many glazes, not a few. Richard Aerni single fires and he adds
bentonite to his.
Linda
Ithaca, NY
Tony Ferguson on sat 14 apr 01
To add further to the single firing:
I add 2-5% bentonite in my glazes and sometimes ball
clay. I may up the ball and reduced the kaolin.
Shinos seem to always work without any problems.
Tony Ferguson, Duluth, Minnesota
--- Linda Blossom wrote:
> > Ron Roy, as usual gives very useful answers. and
> his post on shrinkage
> etc.
> > made this process very clear. I want to add a
> little comment here for
> those
> > contemplating single firing, it is important to
> add a clay component to
> most
> > glazes used in the above process because glazes
> without clay do not shrink
> > as much as the green or re-wetted body being
> glazed and then tend to flake
> > off as the body dries and shrinks.
> > Feri.
>
> Actually, I have never found this to be true. I add
> veegum (a binder) to
> all my glazes and sieve them and have never had a
> problem. I am talking
> about many glazes, not a few. Richard Aerni single
> fires and he adds
> bentonite to his.
>
> Linda
> Ithaca, NY
>
>
______________________________________________________________________________
> 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.
=====
--Tony Ferguson, fergyart@yahoo.com315 N. Lake Ave. Apt 401Duluth, MN 55806(218) 727-6339Looking to see, buy or barter artwork go to:http://acad.uwsuper.edu/www/aferguso/fergyart.htm
vince pitelka on sat 14 apr 01
> Actually, I have never found this to be true (Feri said that a clay
component must be added to single-fire glazes). I add veegum (a binder) to
> all my glazes and sieve them and have never had a problem. I am talking
> about many glazes, not a few. Richard Aerni single fires and he adds
> bentonite to his.
Linda -
Veegum-T is a clay component. It is essentially a refined bentonite
product, and of course bentonite is the finest-particle clay. If you are
using Veegum-Cer, it is a combination of Veegum-T and CMC gum.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Linda Blossom on sun 15 apr 01
In answer to Vince's comments, I do use Veegum-cer.
Ned asked:
Bentonite and Veegum - are they functionally interchangeable? When would you
use one and not the other? Any adhesion issues with overlapping glazes?
Caveats? All raw glazing, single firing enlightenment appreciated!
My answer based on Richard Aerni's experience with bentonite and Vince's
post would be probably yes... I use 1% of Veegum-cer. I always use the
veegum because it has worked for me and I trust it. I am sure Richard feels
the same way about bentonite. . I have found that it helps the glaze deal
with the dry clay layer that can act like little ball bearings. It also
makes the dry glaze much stronger. I do have to sieve the wet glaze. Not
sieving is a good way to guarantee crawling.
I have never had any issues with overlapping glazes. It does thicken a
glaze. I would glaze anything with joinery very carefully. Probably not
all the glaze at once and maybe even part of the glaze on one side of a
piece at a time and then the inside. In other words, if it is a slab built
piece in sections I would glaze a coat, let it dry, add a coat etc. This
comes from the experience of watching pieces pull themselves apart. I
might think this would be different with paperclay. It has been a long time
since this happened to me and was in my pre paperclay days. I would still
proceed with caution.
Linda
Ithaca, NY
My original post:
> > Actually, I have never found this to be true (Feri said that a clay
> component must be added to single-fire glazes). I add veegum (a binder)
to
> > all my glazes and sieve them and have never had a problem. I am talking
> > about many glazes, not a few. Richard Aerni single fires and he adds
> > bentonite to his.
>
> Linda -
> Veegum-T is a clay component. It is essentially a refined bentonite
> product, and of course bentonite is the finest-particle clay. If you are
> using Veegum-Cer, it is a combination of Veegum-T and CMC gum.
> Best wishes -
> - Vince
>
WHC228@AOL.COM on mon 16 apr 01
I have been single firing for about 15 years. I use VeegumT because it is=
a
good suspender, and it is trouble free when it comes to apply another gla=
ze
over it. Additives that are gums dry to form a shell that doesn't absorb =
a
glaze being applied over it as easily. I like to apply several layers of
glazes and do not like to wait for my glazes to dry. I would rather have =
the
water be absorbed into the body. I use markers on my ware boards to indic=
ate
what day that the pot was glazed so that I am not firing a pot that has t=
oo
much water in it.
Someone brought up the issue of the glaze dissolving the body of the pot =
at
the interface better on a raw pot than a bisked one. I bisk some of my mo=
re
complicated shapes, like teapots and casseroles. They amount to about 10%=
of
the total number of pots that I do. There is no noticeable difference bet=
ween
the look and fit of the raw glazed pots from those that I bisk. This coul=
d be
different at lower temperatures. I fire to cone 10.
Bill Campbell
Martin Howard on tue 17 apr 01
Ference reminded us that :-
it is important to add a clay component to most
glazes used in the above process because glazes without clay do not shrink
as much as the green or re-wetted body being glazed and then tend to flake
off as the body dries and shrinks.>
I just spent a long time on 4 good bowls, with heart and other decorations.
I was pleased with them. Then I dipped them in one of my two clear glazes.
It was the one without the 20 clay and catlitter. They just collapsed
because of the differential contraction. :-(( That bucket is now marked NOT
FOR ONCE FIRING.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
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