Lou Raye Nichol on mon 16 aug 10
Hi All
I have had occasional problems with blistering in Malcolm's shino. Often
they are small bubbles and smooth out in refiring, but occasionally they ar=
e
big and beyond recovering. John Britt thinks it can be a release of sodium
oxide at about 2012 F and suggests slowing the kiln around this temp - but
he is not sure because it is intermittant and suggested I write clayart.
Has anyone had this problem? Do you know what causes it and what to do abou=
t
it?
Lou Raye
Lou Raye Nichol
Carbon Trapped Porcelain
919-303-5848
www.louraye.com
pots@louraye.com
William & Susan Schran User on mon 16 aug 10
On 8/16/10 6:34 PM, "Lou Raye Nichol"
wrote:
> Hi All
>
> I have had occasional problems with blistering in Malcolm's shino. Often
> they are small bubbles and smooth out in refiring, but occasionally they =
are
> big and beyond recovering. John Britt thinks it can be a release of sodiu=
m
> oxide at about 2012 F and suggests slowing the kiln around this temp - bu=
t
> he is not sure because it is intermittant and suggested I write clayart.
> Has anyone had this problem? Do you know what causes it and what to do ab=
out
> it?
One cause of bubbles/blisters in glazes comes from the clay.
Bisque fired too fast or not hot enough could release gasses through the
glaze.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Ron Roy on mon 16 aug 10
Hi Lou,
Do all the pots in a firing have the blisters or just some?
Are the blisters on certain areas of the pot - like one side or the
bottom half?
What kind of clay do you use - what cone do you bisque to and in what
kind of kiln?
RR
Quoting Lou Raye Nichol :
> Hi All
>
> I have had occasional problems with blistering in Malcolm's shino. Often
> they are small bubbles and smooth out in refiring, but occasionally they =
are
> big and beyond recovering. John Britt thinks it can be a release of sodiu=
m
> oxide at about 2012 F and suggests slowing the kiln around this temp - bu=
t
> he is not sure because it is intermittant and suggested I write clayart.
>
> Has anyone had this problem? Do you know what causes it and what to do ab=
out
> it?
>
> Lou Raye
>
> Lou Raye Nichol
> Carbon Trapped Porcelain
> 919-303-5848
> www.louraye.com
> pots@louraye.com
>
Paul Herman on mon 16 aug 10
Hi Lou Raye,
I have had spectacular blisters in Malcolm's shino and some other
shinos, in one of our wood firings. I think I tracked it down to
having not enough reduction in the early part of the firing. Because
of that, during the later part of the firing the iron oxide in the
clay body went through a temperature related reduction, giving off
bubbles of gas near the top temperature. It ruined a lot of pots that
were in one area of the kiln which was oxidized. There have
occasionally been bubbles like this in the oxidized corners of my gas
firings, with several different glazes.
So, are your bubbles forming at the last part of the firing, or during
the wet glazing process? Are the bubbles on ware that looks like it
didn't get enough reduction?
best,
Paul Herman
Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/
On Aug 16, 2010, at 3:34 PM, Lou Raye Nichol wrote:
> Hi All
>
> I have had occasional problems with blistering in Malcolm's shino.
> Often
> they are small bubbles and smooth out in refiring, but occasionally
> they are
> big and beyond recovering. John Britt thinks it can be a release of
> sodium
> oxide at about 2012 F and suggests slowing the kiln around this temp
> - but
> he is not sure because it is intermittant and suggested I write
> clayart.
>
> Has anyone had this problem? Do you know what causes it and what to
> do about
> it?
>
> Lou Raye
>
> Lou Raye Nichol
> Carbon Trapped Porcelain
> 919-303-5848
> www.louraye.com
> pots@louraye.com
Dale Neese on tue 17 aug 10
I believe that the blistering, bubbling effect seen in some high fired Shin=
o
glazes are caused by the abundance of soluble materials on the dried glaze
surface. Your Soda Ash content which give Shinos it's characteristic glaze
surface quality. Some Shinos differ in Soda Ash content than others like
Malcolm's carbon trapping Shino glazes that tend to have higher amounts of
Soda Ash. When a Shino glaze dries on a pot the soluble material tend to
migrate to the surface of the glaze in concentration. In thicker
applications the concentrations of the soluble material are more pronounced
and when high fired can produce blisters. The type of Soda Ash, hard or
soft, where and how you store your soluble soda ash (atmospheric water
absorption) has much to do with the resulting glaze quality over time as
the soluble materials leach into the glaze water. The older ( big glaze
bucket refilled less ) the Shino Glaze the more soluble materials have
leached into the water. I have noticed on some of my Shino glazes that the
bigger blisters are crusty, can be broken easily by touch revealing a smoot=
h
circle of grayish clay surface underneath. The bigger blisters occur where
the glaze application is thicker. Smaller blisters had burst and settled
back down to the glaze leaving an nice unusual glaze textural effect.
Blistering usually happens on one side of the pot where the flows of glaze
from dipping are the thickest. Sometimes the blisters are even more
pronounced if a pot edge has been hanging off the shelf into the direct
flame path.
My suggestions to cure blistering in Shinos are to store your Soda Ash in
sealed containers in a less humid environment. Mix your Shinos more often i=
n
smaller batches. However if you don't "age" your Shino glaze some you will
get a more anemic whiter glaze. Fire sooner after Shino glazing. Don't put
your Shino glaze ware into the hotter flame paths in the kiln.
Dale Tex
"across the alley from the Alamo"
Helotes, Texas USA
www.daleneese.com
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