LESAINT1 on mon 23 mar 98
Hello Clayart.
I have been testing this c6 glaze that someone posted variously named
Floating Red and Andrew's oxblood. It has a beautiful varied red-orange color
with dark streaks or a black metallic color with gray-tan and red streaks.
The trouble is I am getting clusters of bubbles, not like regular pinholing,
but more like localized volcanic eruptions. Can anyone explain this or help me
correct it? I have been firing overnight on low , turning up to medium in
the morning( kiln temp 1150 F) for two hours, then to high (takes about 3hrs)
to about 2200F or a good C5, then a 2-hr soak on medium.
The recipe is:
Gerstly Borate 54.88
Talc 14.63
Flint 30.49
Red iron oxide 21.95
The color is so intriguing that I would really like to make this glaze work.
Thanks in advance.
Leslie
Tom Buck on tue 24 mar 98
Hi Leslie: This glaze, with 55% Gerstley Borate, will give trouble because
of the non-uniformity of the GB -- the ore is quite random and uncertain,
and no attempt is made to remove unwanted stuff. The ore is shipped to
sellers as 3-inch pebble, and they pulveriuze it, screen it somewhat, and
bag it. So, GB will vary a bit, bag by bag.
What to do? Well, there is one thing that MIGHT help. I am not
certain what screen the sellers use, but under 50-mesh would not surprise
me, since they are selling by weight and want to keep all the ore in the
powder they can. In the ore Gypsum is a contaminant, and since it is a
harder rock-like material vs the ulexite and colemanite (the two
components of GB), then it tends to stay bigger in size than the other
two. Gypsum is nasty, it spits on firing, makes holes and blisters. And
one never knows how much is present in a bag. But you can lower the odds a
bit by putting the GB through an 80 to 100-mesh screen before use.
Approximately 2.5% will stay on the screen; these larger particles are
Gypsum mostly so just discard same. Now weigh out your glaze and hope for
the best. Good tests. Til later. Tom.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
On Mon, 23 Mar 1998, LESAINT1 wrote:
> ----------------------------Original message----------------------------
> Hello Clayart.
> I have been testing this c6 glaze that someone posted variously named
> Floating Red and Andrew's oxblood. It has a beautiful varied red-orange color
> with dark streaks or a black metallic color with gray-tan and red streaks.
> The trouble is I am getting clusters of bubbles, not like regular pinholing,
> but more like localized volcanic eruptions. Can anyone explain this or help me
> correct it? I have been firing overnight on low , turning up to medium in
> the morning( kiln temp 1150 F) for two hours, then to high (takes about 3hrs)
> to about 2200F or a good C5, then a 2-hr soak on medium.
> The recipe is:
> Gerstly Borate 54.88
> Talc 14.63
> Flint 30.49
> Red iron oxide 21.95
> The color is so intriguing that I would really like to make this glaze work.
> Thanks in advance.
> Leslie
>
Ron Roy on sun 5 apr 98
Hi Leslie,
This could be a bisque firing problem - Tell me what type of clay you are
using and a complete description of your bisque firing from beginning to
end and what cone.
>----------------------------Original message----------------------------
> Hello Clayart.
>I have been testing this c6 glaze that someone posted variously named
>Floating Red and Andrew's oxblood. It has a beautiful varied red-orange color
>with dark streaks or a black metallic color with gray-tan and red streaks.
>The trouble is I am getting clusters of bubbles, not like regular pinholing,
>but more like localized volcanic eruptions. Can anyone explain this or help me
>correct it? I have been firing overnight on low , turning up to medium in
>the morning( kiln temp 1150 F) for two hours, then to high (takes about 3hrs)
>to about 2200F or a good C5, then a 2-hr soak on medium.
>The recipe is:
>Gerstly Borate 54.88
>Talc 14.63
>Flint 30.49
>Red iron oxide 21.95
>The color is so intriguing that I would really like to make this glaze work.
>Thanks in advance.
>Leslie
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
JCapetty on mon 6 apr 98
Leslie,
I tried your floating red glaze and I too got a similar result with clusters
of pinholing bubbles. I bisqued to cone 04 and wondered if I overfired the
glaze firing. Don't think so, since the cones were bent properly and all other
pieces in the firing looked good. I'm anxious to hear the answer to this
question, as the glaze color looks promising!
Janet Capetty
LESAINT1 on tue 7 apr 98
Hi Ron. Thanks for looking at this. I use Standard Ceramic #112 c4-6
speckled brown stoneware. I generally follow the overnight bisque firing
recommended in Zakin's book on electric kiln firing. I start the load about 4
pm on the lowest setting with the lid open for 3 hours. The kiln gets to
about 200F. Then I close the lid and about 2 hours later at about 450F turn it
up to second lowest setting. About 2 hours later I turn it up to 25% power and
leave it on overnight . About 8 am the temp is about 1250 and I turn it up to
medium 50% power for one hour then to high. It reaches c05 after 1-2 hours on
high(about 1950F). That's it. Thanks for the help. Leslie
Ron Roy on fri 10 apr 98
Hi Leslie,
So you are turning your kiln up at 1250F (677C) and off in 3 hours at 1950F
(1065C)
- I talk centigrade - so you are going at about 133C per hour (about 271F
per hr.) too fast. The crucial time is between 700 and 900C (1292 to 1692F)
- if the iron in the body gets reduced from the carbon leaving the clay it
becomes a strong flux. The specks of iron from fire clay for instance will
then over flux the clay around them giving bubbles and blisters. The main
indication that this is happening - if you refire the blisters will still
be there.
All this depends on how much carbon and iron is present in the body, how
tightly stacked the kiln is and - how tight the kiln is. If there is enough
free oxygen in the kiln the Carbon - looking for oxygen - will get it from
the free Oxygen in the kiln. If it can't get it there it will take it from
the Fe2O3 (not a strong flux) in the body making it FeO (a strong flux.)
There are two ways to stop it. Fire slower from 700 to 900C and/or let in
more air by leaving a spy open. I suggest you fire slower. I suggest going
no faster than 65C (150F) per hour during the crucial stage - you may even
need to leave your top spy hole open as well.
There are times when you can go faster - white clays have little iron for
instance. I still feel you will get better (more consistent firing from top
to bottom) with a slower firing.
Let me know if this cures the problem - there is a chance that your some of
your glazes could be a problem - those with Zinc Oxide for instance - Zinc
oxide is easily reduced and can lead to boiling and pinholing.
rr
>----------------------------Original message----------------------------
>Hi Ron. Thanks for looking at this. I use Standard Ceramic #112 c4-6
>speckled brown stoneware. I generally follow the overnight bisque firing
>recommended in Zakin's book on electric kiln firing. I start the load about 4
>pm on the lowest setting with the lid open for 3 hours. The kiln gets to
>about 200F. Then I close the lid and about 2 hours later at about 450F turn it
>up to second lowest setting. About 2 hours later I turn it up to 25% power and
>leave it on overnight . About 8 am the temp is about 1250 and I turn it up to
>medium 50% power for one hour then to high. It reaches c05 after 1-2 hours on
>high(about 1950F). That's it. Thanks for the help. Leslie
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
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