Cindy on thu 2 dec 04
Dear Melissa,
Low fire wares should have all their shrinking and gassing off done and
finished during the bisque firing. When you refire to melt the glaze, you
shouldn't get any further shrinkage in the clay, since it has already been
down that street.
Instructions will vary with the glaze, but for commercial glazes, this is
generally the case. It has to do with glaze fit.
As for color, most low-fire glazes need more than one coat. With practice,
you will learn the thickness you like for each glaze. Just scratch the
surface in an inconspicuous place to see the thickness.
I'm not a low-fire potter, but I hope this helps.
Cindy in SD
Subject: Earthenware Firing
Hello All,
I am about to bisque a kilnful of earthenware bottles I made. This is only
the second time I have worked with earthenware (Sheffield's Mass White,
which is wonderful to work with); it seems to have great potential for
sculptural work for me. HOWEVER, I have question that none of my books
explains:
OK, for all clays we bisque fire on or about ^04 or thereabouts; (I know
there are exceptions) creating a porous, absorbent surface for the glaze.
For high fire clays, we then proceed to a glost firing of ^5 to ^10; BUT WHY
do we fire earthenware at a LOWER temperature in the glost fire?
Instructions on commercial low-fire glazes commonly specifies a glaze firing
temp. of ^06. It seems more logical to fire the bisque at ^06 or far lower
(for more porosity) and fire the glaze at closer to ^04. Wouldn't there be
better absorption of the color?
Also, can oxides be used on earthenware bisque as a plain wash, or should
they be coated with a clear coat of low-fire glaze? Or should they be used
at all??
Thank you all so much. Clayart is a dream come true!!!
Best,
Melissa Jeswald Dec
Boxford, MA
k.dec@comcast.net
____________________________________________________________________________
__
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.
kenneth dec on thu 2 dec 04
Hello All,
I am about to bisque a kilnful of earthenware bottles I made. This is =
only the second time I have worked with earthenware (Sheffield's Mass =
White, which is wonderful to work with); it seems to have great =
potential for sculptural work for me. HOWEVER, I have question that none =
of my books explains:
OK, for all clays we bisque fire on or about ^04 or thereabouts; (I know =
there are exceptions) creating a porous, absorbent surface for the =
glaze. For high fire clays, we then proceed to a glost firing of ^5 to =
^10; BUT WHY do we fire earthenware at a LOWER temperature in the glost =
fire? Instructions on commercial low-fire glazes commonly specifies a =
glaze firing temp. of ^06. It seems more logical to fire the bisque at =
^06 or far lower (for more porosity) and fire the glaze at closer to =
^04. Wouldn't there be better absorption of the color?
Also, can oxides be used on earthenware bisque as a plain wash, or =
should they be coated with a clear coat of low-fire glaze? Or should =
they be used at all??
Thank you all so much. Clayart is a dream come true!!!
Best,
Melissa Jeswald Dec
Boxford, MA=20
k.dec@comcast.net
Cindi Anderson on fri 3 dec 04
Hi
The reason is that earthenware never vitrifies at those temperatures; it is
always porous. So there is no need to fire low to maintain porosity. On
the other hand, by firing the bisque hotter than the glaze, you can burn out
more impurities so they are less likely to come out during the glaze firing
(which is cooler) causing glaze defects.
Cindi
----- Original Message ----- OK, for all clays we bisque fire on or about
^04 or thereabouts; (I know there are exceptions) creating a porous,
absorbent surface for the glaze. For high fire clays, we then proceed to a
glost firing of ^5 to ^10; BUT WHY do we fire earthenware at a LOWER
temperature in the glost fire? Instructions on commercial low-fire glazes
commonly specifies a glaze firing temp. of ^06. It seems more logical to
fire the bisque at ^06 or far lower (for more porosity) and fire the glaze
at closer to ^04. Wouldn't there be better absorption of the color?
Malcolm Schosha on fri 3 dec 04
Melissa,
With earthenware, if you bisque low and glaze high the glaze will
craze...always.
I would not recommend using oxides for puting on washes, unless (for
some reason) there is no choice. Many oxides are quite toxic. Better
to use glaze stains where the oxides are fritted, and safer to use.
Malcolm Schosha
--- In clayart@yahoogroups.com, kenneth dec wrote:
> Hello All,
>
> I am about to bisque a kilnful of earthenware bottles I made. This
is only the second time I have worked with earthenware (Sheffield's
Mass White, which is wonderful to work with); it seems to have great
potential for sculptural work for me. HOWEVER, I have question that
none of my books explains:
>
> OK, for all clays we bisque fire on or about ^04 or thereabouts; (I
know there are exceptions) creating a porous, absorbent surface for
the glaze. For high fire clays, we then proceed to a glost firing of
^5 to ^10; BUT WHY do we fire earthenware at a LOWER temperature in
the glost fire? Instructions on commercial low-fire glazes commonly
specifies a glaze firing temp. of ^06. It seems more logical to fire
the bisque at ^06 or far lower (for more porosity) and fire the glaze
at closer to ^04. Wouldn't there be better absorption of the color?
>
> Also, can oxides be used on earthenware bisque as a plain wash, or
should they be coated with a clear coat of low-fire glaze? Or should
they be used at all??
>
> Thank you all so much. Clayart is a dream come true!!!
>
> Best,
> Melissa Jeswald Dec
> Boxford, MA
> k.dec@c...
>
>
______________________________________________________________________
________
> Send postings to clayart@l...
>
> 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@p...
Edouard Bastarache Inc. on fri 3 dec 04
Malcom,
"With earthenware, if you bisque low and glaze high the glaze will
craze...always."
not always.
I fired last summer 5 glazes at c/04, some on commercial clays
and some on local clay.
Pots were bisque fired at c/08 with my other stoneware pots.
Included was a long range glaze, from c/04 to c/9.
No crazing !!!
If you want to see pix of this firing I have a zipped file in store.
Later,
"Ils sont fous ces quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Snail Scott on sat 4 dec 04
>...WHY
>do we fire earthenware at a LOWER temperature in the glost fire?
>Instructions on commercial low-fire glazes commonly specifies a glaze firing
>temp. of ^06. It seems more logical to fire the bisque at ^06 or far lower
>(for more porosity) and fire the glaze at closer to ^04.
Most earthenware never becomes sufficiently non-porous
to interfere with glaze absorption unless fired well
above standard earthenware temperatures, so the higher
bisque temperature is not an issue. What is an issue,
however, is that many colorants used in commercial
low-fire glazes are sensitive to the outgassing of the
materials in the clay. By firing the bisque hotter than
the eventual glaze firing, you accomplish most or all
of the outgassing that might be a problem. Some glazes
are not much affected by outgassing, but reds and oranges
are especially vulnerable. If you never use these colors,
you may be able to bisque lower, but it really won't
gain you much advantage, either.
>Also, can oxides be used on earthenware bisque as a plain wash, or should
>they be coated...
Oxide washes work just dandy on earthenware - no need
for glaze or sealants unless you like it that way.
Some oxides are somewhat refractory, though, and will
bond better at low temperatures with a pinch of flux
added to the wash.
-Snail Scott
| |
|
