Jeff Lawrence on sun 21 jan 01
Hello Clayart,
Here's something that stumps me -- any theories welcome.
I mixed up a 20 lb batch of white glaze and found it fired a good clean
white. A month or so later, the water of settlement was tobacco spit brown.
I figured something got dumped into it by accident and mixed a new batch.
After a month, that one, too, had the brown bilgewater condition.
When I mix the brown juice back in and sieve, the white is still okay,
albeit with somewhat the look of overdeflocculated slip when dry -- tan
edges on the first things to dry.
If I don't mix, there appear to be brown flecks on it when I spray, and
vestigial brown flecks persist after firing.
The glaze:
04RRA3J -- zinc-free 04 base REV A3 (04RRA3jA)
==============================================
FRIT 3134........... 5.77 27.16%
NEPHELINE SYENITE... 4.58 21.54%
WOLLASTONITE........ 6.37 29.97%
ZIRCOPAX............ 2.49 11.72%
OM #4 BALL CLAY..... 1.00 4.68%
Macaloid............ 0.30 1.41%
LITHIUM CARBONATE... 0.40 1.88%
VEEGUM T............ 0.35 1.65%
========
21.25
What's going on?
Jeff Lawrence ph. 505-753-5913
18496 US HWY 84/285 fx. 505-753-8074
Espanola, NM 87532 jml@cybermesa.com
Snail Scott on mon 22 jan 01
At 11:18 PM 1/21/01 -0700, you wrote:
>Hello Clayart,
>
>the water of settlement was tobacco spit brown.
> -- tan edges on the first things to dry.
>
>Jeff Lawrence
I have a glaze that does that, too. An ancient
batch of vitreous engobe containing the last
of my Albany Slip. The only ingredients it has
in common with Jeff's glaze are OM-4 ball clay
and lithium carbonate. It exhibits the dry-tan-
edge phenomenon also noticed by Jeff. It still
fires the same as always after I mix it, though.
(Still looks nice, too. I sent Janet Kaiser a
tile for the Potters Path using some of it.)
-Snail
Cindy Strnad on mon 22 jan 01
Hi, Jeff.
Am I reading your post correctly? I hear you saying you get a brownish
discoloration of your glaze in the bucket and on your unfired pots, but the
glaze, when fired, is white.
I've experienced the same thing, in a lesser degree, with Tony Hansen's 5x5
glaze (20% each of silica, epk, custer spar, frit 3134, and wollastonite)
when I use it with 7% added zircopax for a semi-opaque white. Instead of
brown, I get a yellowish color on my dried, unfired pieces. This isn't
noticeable in the glaze bucket.
I wonder if it isn't caused by some sort of biological activity in my water.
I use well water. No chlorine. There's a bit of manganese (not much) and
iron (again, not much) and tannic acid (rather a lot) in this water.
Ideally, I should be using distilled water, but I'm not picky about getting
a perfect white, and have never had anything I'd regard as trouble with it.
Still, I wonder if it (the tannic acid, or some kind of little beasties
beginning to establish their presence) isn't responsible for the yellow cast
I see on my raw, glazed pieces. There's no unusual smell.
Anyway, if you're using plain water, especially non-chlorinated water, maybe
that has something to do with your strange phenomenon. The water does change
a bit, with the rise and fall of the water table, so you wouldn't
necessarily always experience the same sorts of effects.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
Janet Kaiser on mon 22 jan 01
I can second that! A very nice glaze... And on a
beautiful tile for The Path... Also the one and
only example of a tile glazed with the famous
Albany Slip! It is being cherished, Snail! Will
be in a prominent part of The Path, so I can
point it out to UK potters easily... We all know
about Albany Slip, but never used any. For some
reason I always thought it was a very dark,
shiny brown, like Bristol ware.
Janet Kaiser
The Chapel of Art . Capel Celfyddyd
HOME OF THE INTERNATIONAL POTTERS' PATH
Criccieth LL52 0EA, GB-Wales Tel: (01766) 523570
E-mail: postbox@the-coa.org.uk
WEBSITE: http://www.the-coa.org.uk
----- Original Message -----
From: Snail Scott
> I have a glaze that does that, too. An ancient
> batch of vitreous engobe containing the last
> of my Albany Slip. The only ingredients it has
> in common with Jeff's glaze are OM-4 ball clay
> and lithium carbonate. It exhibits the
dry-tan-
> edge phenomenon also noticed by Jeff. It still
> fires the same as always after I mix it,
though.
>
> (Still looks nice, too. I sent Janet Kaiser a
> tile for the Potters Path using some of it.)
Mike Gordon on mon 22 jan 01
Hi,
I always thought that a yellowish discoloration on dried, unfired white
glaze was caused by sulphur in the clay seeping out, or some impurity in
the clay. It always fires out. Mike Gordon
Logan Oplinger on tue 23 jan 01
Jeff:
The brown color in the water is from the organics in the OM # 4 ball clay. Had same happen to me w/ some casting slip.
Try this crude test;
Mix some OM #4 w/ water to make a thin slip, defloc w/ about 1-2% soda ash, let settle & observe results.
Logan Oplinger
---- you wrote:
> I mixed up a 20 lb batch of white glaze and found it fired a good clean
> white. A month or so later, the water of settlement was tobacco spit brown.
> I figured something got dumped into it by accident and mixed a new batch.
> After a month, that one, too, had the brown bilgewater condition.
.....
> The glaze:
> 04RRA3J -- zinc-free 04 base REV A3 (04RRA3jA)
> ==============================================
> FRIT 3134........... 5.77 27.16%
> NEPHELINE SYENITE... 4.58 21.54%
> WOLLASTONITE........ 6.37 29.97%
> ZIRCOPAX............ 2.49 11.72%
> OM #4 BALL CLAY..... 1.00 4.68%
> Macaloid............ 0.30 1.41%
> LITHIUM CARBONATE... 0.40 1.88%
> VEEGUM T............ 0.35 1.65%
> ========
> 21.25
>
> What's going on?
>
> Jeff Lawrence ph. 505-753-5913
> 18496 US HWY 84/285 fx. 505-753-8074
> Espanola, NM 87532 jml@cybermesa.com
------------------------------------------------------
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ferenc jakab on tue 23 jan 01
>
> I've experienced the same thing, in a lesser degree, with Tony Hansen's
5x5
> glaze (20% each of silica, epk, custer spar, frit 3134, and wollastonite)
> when I use it with 7% added zircopax for a semi-opaque white. Instead of
> brown, I get a yellowish color on my dried, unfired pieces. This isn't
> noticeable in the glaze bucket.
Cindy,
If you are talking about raw fired pieces on earthenware or terracotta clay,
then I have experienced a similar thing. The glaze developing a brownish
scum when the piece dries. I believe that this is iron and other salts
coming up through the glaze while the piece is drying. I believe this was
one of the reasons the ancient Arabs developed bisque firing for Maiollica
ware. The only way I have been able to avoid this is to glaze when at the
driest limit of leather hard. I'm talking about two or three firings only
and so cannot guarantee that this is always the solution.
Feri
Jeff Lawrence on wed 24 jan 01
Hello again,
Thanks for the brain cycles -- I'm glazing white earthenware (50:50 ball
clay:talc), so don't think salts seeping through are the problem.
What puzzles me is why the color doesn't all fire out? Next batch I'll use
EPK instead of OM4 and probably watch the mystery disappear, but meanwhile,
I'm still wondering.
Jeff Lawrence ph. 505-753-5913
18496 US HWY 84/285 fx. 505-753-8074
Espanola, NM 87532 jml@cybermesa.com
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