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pinholes, craters, and blisters, gas, vs electric raku

updated fri 18 apr 03

 

Leland G. Hall on sun 13 apr 03


Hello to all potters,

In an attempt to increase productivity I recently switched back to gas
fireing for raku. I had too many dificulties with pinhoes, craters and
blisters when firing with my first top hat gas kiln. Then I took a workshop
with some folks that have been raku fireing full time since the early
seventies. They fire exclusively with electric. Claim much more
consistent results that way. So I tried it. Have been firing electric
raku full time for a couple of years, with great results. No more glaze
defects.

Like I said, I just recently put a new gas kiln on line in the shed. An
old skutt conversion. Same bisque. Same glaze. Fire real slow.
Pyrometer, and cone too. Glaze melts. Pinholes. Blisters. Craters. Not
always, but way too oftern.

Now here's the kicker. I pulled a couple of pots yesterday out of the
electric kiln, great glaze melt, but I did not get the reduction I wanted.
Understand please, these two pots had a perfect glassy glaze melt.

I made a descision to refire them, with a stronger post-firing reduction
following. I thought, why not go for the new gas kiln? Surly if I go
slow, it wont screw up this already nicely matured glaze. Just re-melt it,
and go for new reduction process.

Wrong. Craters and blisters. Just like what usually happens with a newly
glazed pot in my gas kiln. How can this be? Same cone. (^8) Same
pyrometer reading. Apparently, there is something about fuel firing that I
don't know or don't understand. My glaze matures around ^08, and I bisque
at ^04 or ^05. Glaze is all 80/20 gb/ neph sy. And always works great in
the electric kiln. What the dickens is going on here!!?? Please help any
one with any ideas. I really need to nail down this gas firing thing. I
can't keep up with sales. I need to make this work.

Thank you all, and best wishes
Leland Hall
Before the Wheel Enterprises
La Pine OR


PS. It's not claybody related. Same clay works fine my electric, not in
ither gas kiln.

Gary Ferguson on sun 13 apr 03


Leland:

Ok, I have one guess. The electric kiln is firing in oxidation and maybe
the gas kiln is firing in reduction. Could the reduction process be forcing
gas from the clay body to produce the defects you describe?

Gary Ferguson
Raku Clay Artist
Nampa, ID 83687
Visit my site at http://www.garyrferguson.com
Subscribe to Just Raku Newsletter at http://www.JustRaku.com

Carole Fox on mon 14 apr 03


Leland,
I suspect it is the GB in your glaze that is causing you trouble. Or perhaps
you are overfiring? If you can see into the kiln during the firing, you will
see the bubbles (which become pinholes) as black dots on the surface of your
glaze. As soon you see this happening, turn down the gas and soak the kiln
until the black dots disappear. Then, a brief raising of the temperature
should smooth out the surface of the glaze.

GB raku glazes can really be a pain. You may have more success with this
glaze base:
3134 frit 90
EPK 10
To this, I add a little epsom salt.
Best of luck!
Carole Fox
Elkton, MD
thesilverfox@dol.net
----- Original Message -----
From: "Leland G. Hall"
To:
Sent: Sunday, April 13, 2003 5:10 PM
Subject: pinholes, craters, and blisters, gas, vs electric raku


> Hello to all potters,
>
> In an attempt to increase productivity I recently switched back to gas
> fireing for raku. I had too many dificulties with pinhoes, craters and
> blisters when firing with my first top hat gas kiln. Then I took a
workshop
> with some folks that have been raku fireing full time since the early
> seventies. They fire exclusively with electric. Claim much more
> consistent results that way. So I tried it. Have been firing electric
> raku full time for a couple of years, with great results. No more glaze
> defects.
>
> Like I said, I just recently put a new gas kiln on line in the shed. An
> old skutt conversion. Same bisque. Same glaze. Fire real slow.
> Pyrometer, and cone too. Glaze melts. Pinholes. Blisters. Craters.
Not
> always, but way too oftern.
>
> Now here's the kicker. I pulled a couple of pots yesterday out of the
> electric kiln, great glaze melt, but I did not get the reduction I wanted.
> Understand please, these two pots had a perfect glassy glaze melt.
>
> I made a descision to refire them, with a stronger post-firing reduction
> following. I thought, why not go for the new gas kiln? Surly if I go
> slow, it wont screw up this already nicely matured glaze. Just re-melt
it,
> and go for new reduction process.
>
> Wrong. Craters and blisters. Just like what usually happens with a newly
> glazed pot in my gas kiln. How can this be? Same cone. (^8) Same
> pyrometer reading. Apparently, there is something about fuel firing that
I
> don't know or don't understand. My glaze matures around ^08, and I bisque
> at ^04 or ^05. Glaze is all 80/20 gb/ neph sy. And always works great in
> the electric kiln. What the dickens is going on here!!?? Please help any
> one with any ideas. I really need to nail down this gas firing thing. I
> can't keep up with sales. I need to make this work.
>
> Thank you all, and best wishes
> Leland Hall
> Before the Wheel Enterprises
> La Pine OR
>
>
> PS. It's not claybody related. Same clay works fine my electric, not in
> ither gas kiln.
>
>
____________________________________________________________________________
__
> 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.

Liz Gowen on mon 14 apr 03


Leland, the teacher I had several summers ago for Raku would. once the
glazes looked glossy through the peep hole he backed off the gas flow a bit
and let it soak , maybe 10 minutes before taking the pieces out. We also
used the 80/20 glazes you mentioned and they came out well.
I have had a gerstley glaze that was smooth at ^6 get all blistered
when I refired in a bisque ^04( without a soak.to try to bring out the red
in another glaze on the same piece ) I would have thought all the gasses
escaped on the first firing. I believe it is the gerstley but I don't know
chemically what is going on.
Good luck
Liz Gowen

> Wrong. Craters and blisters. Just like what usually happens with a newly
> glazed pot in my gas kiln. How can this be?

Ababi on mon 14 apr 03


hello Leland
Some raku glazes develop these pinholes, craters, and blisters, as part of their
development. You must waite longer until they will seatle down and your glaze will be
ready
Ababi
-

Snail Scott on mon 14 apr 03


At 05:10 PM 4/13/03 -0400, you wrote:
>...Craters and blisters. Just like what usually happens with a newly
>glazed pot in my gas kiln. How can this be? Same cone. (^[0?]8) Same
>pyrometer reading. Apparently, there is something about fuel firing that I
>don't know or don't understand. My glaze matures around ^08, and I bisque
>at ^04 or ^05. Glaze is all 80/20 gb/ neph sy. And always works great in
>the electric kiln...


Just a guess...gas usually heats up faster than electric.
Are your gas firings faster than your electric firings?
If you are firing by cones, I'm not surprised that the
air around the cone is reaching temperature before the
glaze is fully melted on the clay. Most glazes go through
a phase of bubbling before they smooth out in the end,
and if the work is pulled too soon, those bubbles remain
as blisters and craters. This happens even if a well-
matured glaze is refired. I know of almost no one who
fires raku by cones, because of the need to see that
bubbling phase, and more importantly, to see when it's
over. Forget the cones. Just look at the ware before you
pull it out. Give it the time it needs to smooth over.

-Snail

Tony Hansen on mon 14 apr 03


High boron glazes blister for reasons other than gassing,
fast fire is all the range in industry and they minimize
the boron content as much as possible. GB is higher in
boron than almost any frit I know of. Are these 80%
GB. If they are that is too much.

> Leland, the teacher I had several summers ago for Raku would. once the
> glazes looked glossy through the peep hole he backed off the gas flow a bit
> and let it soak , maybe 10 minutes before taking the pieces out. We also
> used the 80/20 glazes you mentioned and they came out well.
> I have had a gerstley glaze that was smooth at ^6 get all blistered
> when I refired in a bisque ^04( without a soak.to try to bring out the red
> in another glaze on the same piece ) I would have thought all the gasses
> escaped on the first firing. I believe it is the gerstley but I don\'t know
> chemically what is going on.
> Good luck
> Liz Gowen
> > Wrong. Craters and blisters. Just like what usually happens with a newly
> > glazed pot in my gas kiln. How can this be?

========
Tony Hansen

Chris Schafale on mon 14 apr 03


Why do high boron glazes blister, then? I'm trying to deal with this
problem in a glaze I use, which is 50% frit 3134.

Chris

Date sent: Mon, 14 Apr 2003 16:28:14 -0400
Send reply to: Clayart
From: Tony Hansen
Subject: Re: pinholes, craters, and blisters, gas, vs electric
raku
To: CLAYART@LSV.CERAMICS.ORG

> High boron glazes blister for reasons other than gassing,
> fast fire is all the range in industry and they minimize
> the boron content as much as possible. GB is higher in
> boron than almost any frit I know of. Are these 80%
> GB. If they are that is too much.
>
> > Leland, the teacher I had several summers ago for Raku would. once the
> > glazes looked glossy through the peep hole he backed off the gas flow a bit
> > and let it soak , maybe 10 minutes before taking the pieces out. We also
> > used the 80/20 glazes you mentioned and they came out well.
> > I have had a gerstley glaze that was smooth at ^6 get all blistered
> > when I refired in a bisque ^04( without a soak.to try to bring out the red
> > in another glaze on the same piece ) I would have thought all the gasses
> > escaped on the first firing. I believe it is the gerstley but I don\'t know
> > chemically what is going on.
> > Good luck
> > Liz Gowen
> > > Wrong. Craters and blisters. Just like what usually happens with a newly
> > > glazed pot in my gas kiln. How can this be?
>
> ========
> Tony Hansen
>
> ______________________________________________________________________________
> 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.
>


--
Light One Candle Pottery
Fuquay-Varina, North Carolina, USA
(south of Raleigh, NC)
www.lightonecandle.com
candle@intrex.net

Tony Hansen on tue 15 apr 03


> Why do high boron glazes blister, then?

I have always puzzled over this, especially the tendency
of high boron glazes to blister worse on a second firing.
Here is a shot at it, anyone thing I am sounding
ridiculous on this:

Boron can induce blistering, especially if its amount is
quite high (check limit/target formulas for guidance). The
reasons for this phenomenon are not because of gassing (this
is demonstrated by the fact that high boron glazes often
blister worse on a second firing). Boron is a glass like
silica and it wants to form its own glass structures. High
boron can thus cause phase separation (areas of
discontinuous glass chemistry in the fired glaze, e.g.
globules of a sodium borate glass in a calcium silicate
glass matrix). Considering the important function of alumina
in glass structure, the lack thereof would be an agravating
factor in the separation. Phase boundary phenomenon and the
differences in surface tension and melt fluidity of the
phases could breed blisters. This process likely continues
in a second firing (this accounts for blistering getting
worse). Ferro Frit 3134, for example, has no alumina, lots
of boron and plenty of CaO/Na2O, glazes high in it make
ideal candidates for this phase separation.

Here is more information on Frit 3134:

http://digitalfire.ab.ca/cermat/ceramicmaterials/material.php?id=351

> trying to deal with problem in a glaze I use, it is 50% frit 3134.

50% Frit 3134 is way too much in a cone 6 glaze.
The 50:30:20 glaze is not balanced even thought so many people
use it. The 20x5 recipe has only 20% of this frit and melts
fine.
http://digitalfire.ab.ca/cermat/education/114.php


> Chris
> Date sent: Mon, 14 Apr 2003 16:28:14 -0400
> Send reply to: Clayart
> From: Tony Hansen
> Subject: Re: pinholes, craters, and blisters, gas, vs electric
> raku
> To: CLAYART@LSV.CERAMICS.ORG
> > High boron glazes blister for reasons other than gassing,
> > fast fire is all the range in industry and they minimize
> > the boron content as much as possible. GB is higher in
> > boron than almost any frit I know of. Are these 80%
> > GB. If they are that is too much.
> >
> > > Leland, the teacher I had several summers ago for Raku would. once the
> > > glazes looked glossy through the peep hole he backed off the gas flow a bit
> > > and let it soak , maybe 10 minutes before taking the pieces out. We also
> > > used the 80/20 glazes you mentioned and they came out well.
> > > I have had a gerstley glaze that was smooth at ^6 get all blistered
> > > when I refired in a bisque ^04( without a soak.to try to bring out the red
> > > in another glaze on the same piece ) I would have thought all the gasses
> > > escaped on the first firing. I believe it is the gerstley but I don\'t know
> > > chemically what is going on.
> > > Good luck
> > > Liz Gowen
> > > > Wrong. Craters and blisters. Just like what usually happens with a newly
> > > > glazed pot in my gas kiln. How can this be?
> >
> > ========
> > Tony Hansen
> >
> > ______________________________________________________________________________
> > 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.
> >
>
> --
> Light One Candle Pottery
> Fuquay-Varina, North Carolina, USA
> (south of Raleigh, NC)
> www.lightonecandle.com
> candle@intrex.net
>

========
Tony Hansen

Megan Ratchford on tue 15 apr 03


John Hesselberth wrote:

To me is seems
> there is a compositional range where blistering is more likely but on
> either side of that range blistering is not a problem.


Hi John and all the clayart family!
We are having a bit of a quandry with the raku glazes at the studio
where I teach. Recently we have switched from gersley borate to gellespie
borate in a one to one ratio in all of our raku glazes. Over the period of
a couple weeks after making freash batches all of the glazes become harder
and harder to brush on making application clumpy. When the glaze-loaded
brush touches the pot it actually sticks as if the water is absorbed rapidly
leaving a glob of glaze. When this begins to happen we know that we are a
few days away from not being able to use this glaze as it will foam an inch
off the pot. These are blisters upon blisters and looks like that spray
foam that hardens in door and wall cracks...
I'm not listing any recipies because this happens with all of our glazes
whether we have a frit flux or a semi-matt glaze. The only thing I can come
up with is that some vital element of the gellespie is water soluable and is
used up to the point that the glaze formula is no longer stable...
Really I have no clue...Any thoughts???
Megan Ratchford in wet and windy Colorado

John Hesselberth on tue 15 apr 03


On Tuesday, April 15, 2003, at 12:42 AM, Tony Hansen wrote:

> Boron can induce blistering, especially if its amount is
> quite high (check limit/target formulas for guidance). The
> reasons for this phenomenon are not because of gassing (this
> is demonstrated by the fact that high boron glazes often
> blister worse on a second firing)

Hi Tony,

You may be close to an answer here, but I don't think it is complete.
For example, Waterfall Brown (in Mastering Cone 6 Glazes, p 106, 107)
has an extremely high boron level (over .7) and shows no tendency to
blister. On the other hand Waxwing (p 104, 105) has 0.42 boron and is
prone to blister if it is overfired or on too thick. To me is seems
there is a compositional range where blistering is more likely but on
either side of that range blistering is not a problem. I have also
encountered blistering with the Waterfall base but when fairly high
levels of cobalt and/or copper were used as colorants instead of iron.
It is a very complex phenomena which would probably require a
multi-dimensional composition diagram and years of careful
experimentation to sort out.

Regards,

John

http://www.frogpondpottery.com
http://www.masteringglazes.com

iandol on wed 16 apr 03


Dear Tony,
Your view that there might be phase separation due to the conflict =
between Silicate base vitreous solution and a Borate base Solution may =
well be true. It is plausible the boundaries between the two solutions =
would be places where inclusions might concentrate.
However, we need to postulate a source of the gas. To do this I would =
need to know more about the glazes in question and if this phenomenon of =
blistering is noted where glazes do not contain any colouring agents. If =
those who have suffered from this could supply that information I might =
be able to go further.
Best regards,
Ivor Lewis. Redhill, South Australia.

Edouard Bastarache on wed 16 apr 03


Hello all,

I have a few 04 glazes containing large amounts of boron-bearing materials,
such as Gerstley Borate and Ferro frit #3134, and they all work well.
Some at 80% #3134 and 70% Gerstley.

Later,



"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm

----- Original Message -----
From: John Hesselberth
To:
Sent: Tuesday, April 15, 2003 9:11 PM
Subject: Re: pinholes, craters, and blisters, gas, vs electric raku


> On Tuesday, April 15, 2003, at 12:42 AM, Tony Hansen wrote:
>
> > Boron can induce blistering, especially if its amount is
> > quite high (check limit/target formulas for guidance). The
> > reasons for this phenomenon are not because of gassing (this
> > is demonstrated by the fact that high boron glazes often
> > blister worse on a second firing)
>
> Hi Tony,
>
> You may be close to an answer here, but I don't think it is complete.
> For example, Waterfall Brown (in Mastering Cone 6 Glazes, p 106, 107)
> has an extremely high boron level (over .7) and shows no tendency to
> blister. On the other hand Waxwing (p 104, 105) has 0.42 boron and is
> prone to blister if it is overfired or on too thick. To me is seems
> there is a compositional range where blistering is more likely but on
> either side of that range blistering is not a problem. I have also
> encountered blistering with the Waterfall base but when fairly high
> levels of cobalt and/or copper were used as colorants instead of iron.
> It is a very complex phenomena which would probably require a
> multi-dimensional composition diagram and years of careful
> experimentation to sort out.
>
> Regards,
>
> John
>
> http://www.frogpondpottery.com
> http://www.masteringglazes.com
>
>
____________________________________________________________________________
__
> 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.

John Hesselberth on wed 16 apr 03


Hi Megan,

Your theory sounds like a good one, but there may be other reasons
also. Why not try to convert one of them to using a frit instead of
Gillespie Borate and see if the same thing happens. If you want some
help doing that, send me one of your recipes off line and I'll see what
I can come up with.

Regards,

John

On Wednesday, April 16, 2003, at 12:14 AM, Megan Ratchford wrote:

> The only thing I can come
> up with is that some vital element of the gellespie is water soluable
> and is
> used up to the point that the glaze formula
http://www.frogpondpottery.com
http://www.masteringglazes.com

Tony Hansen on wed 16 apr 03


Very interesting. I agree that there are interactions
involved. Perhaps the waterfall brown chemistry is deficient
in the other oxides that are part of the picture. It is a
boron combined with something glass that is separating from
a silica combined with something glass. Eppler deals
with this in his glaze book on page 261 I think. I have spoken
with him many times and he is one of the people that warned
me about this. He says I use too much boron, yet I think
I am pretty conservative.

> > Boron can induce blistering, especially if its amount is
> > quite high (check limit/target formulas for guidance). The
> > reasons for this phenomenon are not because of gassing (this
> > is demonstrated by the fact that high boron glazes often
> > blister worse on a second firing)
> Hi Tony,
> You may be close to an answer here, but I don\'t think it is complete.
> For example, Waterfall Brown (in Mastering Cone 6 Glazes, p 106, 107)
> has an extremely high boron level (over .7) and shows no tendency to
> blister. On the other hand Waxwing (p 104, 105) has 0.42 boron and is
> prone to blister if it is overfired or on too thick. To me is seems
> there is a compositional range where blistering is more likely but on
> either side of that range blistering is not a problem. I have also
> encountered blistering with the Waterfall base but when fairly high
> levels of cobalt and/or copper were used as colorants instead of iron.
> It is a very complex phenomena which would probably require a
> multi-dimensional composition diagram and years of careful
> experimentation to sort out.
> Regards,
> John
> http://www.frogpondpottery.com
> http://www.masteringglazes.com
> ______________________________________________________________________________
> 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 Hansen

Tony Hansen on wed 16 apr 03


There is a chapter in the lessons section of the INSIGHT
manual on this. It deals with the merits of using a frit
vs. a natural source of boron, namely Ulexite and shows
you how to do the substitute.

> Megan Ratchford wrote:
> > The only thing I can come
> > up with is that some vital element of the gellespie is water soluable
> > and is used up to the point that the glaze formula.

========
Tony Hansen

Tom Buck on thu 17 apr 03


Tony H:
If you check, the Boron atom tops the list of glass-formers ....
see Page 301+ Cardew, 1st edn., Pioneer Pottery. and most raku glaze mixes
contain as you noted lots of B2O3 (frit or gerstley borate or equivalent).
And such mixes usually contain some potash spar or soda spar. Hence alkali
metal borate glass forms at lower temperatures than alumino-silicate
glass, and there will TWO liquid glasses in the molten liquidus as C08 (or
higher) is approached. Because of geometric considerations, the two
glasses are not compatible (they prefer to be immiscible). as a result
distinct boundaries occur between the two glasses as the molten glaze
cools past the softening points. which is what you suggested can happen
and on some claybodies, the glaze defects noted above (pinholes, etc.)
will make for unwanted results for some raku potters (but nice
accidentals for others).
When I raised the silica content on raku lustres, the "defects"
did not occur (as noted in my article on one of your websites).
good pots. peace. Tom.

Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada

Edouard Bastarache on thu 17 apr 03


Hello Tom,

excellent explanation, it fills a hole in my knowledge.


"À la revoyure",



"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm

----- Original Message -----
From: Tom Buck
To:
Sent: Thursday, April 17, 2003 12:05 AM
Subject: Re: pinholes, craters, and blisters, gas, vs electric raku


> Tony H:
> If you check, the Boron atom tops the list of glass-formers ....
> see Page 301+ Cardew, 1st edn., Pioneer Pottery. and most raku glaze mixes
> contain as you noted lots of B2O3 (frit or gerstley borate or equivalent).
> And such mixes usually contain some potash spar or soda spar. Hence alkali
> metal borate glass forms at lower temperatures than alumino-silicate
> glass, and there will TWO liquid glasses in the molten liquidus as C08 (or
> higher) is approached. Because of geometric considerations, the two
> glasses are not compatible (they prefer to be immiscible). as a result
> distinct boundaries occur between the two glasses as the molten glaze
> cools past the softening points. which is what you suggested can happen
> and on some claybodies, the glaze defects noted above (pinholes, etc.)
> will make for unwanted results for some raku potters (but nice
> accidentals for others).
> When I raised the silica content on raku lustres, the "defects"
> did not occur (as noted in my article on one of your websites).
> good pots. peace. Tom.
>
> Tom Buck ) -- primary address.
> "alias" or secondary address.
> tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
> mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
>
>
____________________________________________________________________________
__
> 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 Hansen on thu 17 apr 03


I sent off some emails today to people about this,
hopefully I can report back. I was under the impression
that these could be caused by something as simple as
failure to create a dense laydown of the glaze or
boiling related to sites of discontinuous chemical
makeup associated with phase separation.

> Dear Tony,
> Your view that there might be phase separation due to the conflict =
> between Silicate base vitreous solution and a Borate base Solution may =
> well be true. It is plausible the boundaries between the two solutions =
> would be places where inclusions might concentrate.
> However, we need to postulate a source of the gas. To do this I would =
> need to know more about the glazes in question and if this phenomenon of =
> blistering is noted where glazes do not contain any colouring agents. If =
> those who have suffered from this could supply that information I might =
> be able to go further.
> Best regards,
> Ivor Lewis. Redhill, South Australia.
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========
Tony Hansen