Ingeborg Foco on fri 28 dec 07
I am wondering if any of you have ever used "Van Guilder Wood Ash" ^10
Reduction? It is published in John Britt's High fire Glaze book under Ash
Glazes.
I did some tests and I liked the results. Then I made a larger batch and
glazed quite a few pots and had pretty horrible results. (I know you should
work for a long
period of time with a new glaze to work out all of the bugs but I'm always
pushing the envelope and anxious to add something new to my gallery display)
Most of the pots ran heavily and had large craters and or blisters. Most
everything has gone into the trash. Some items I am planning on
re firing to see what will happen. My firing was longer than normal (that's
another story) and because I was afraid the glaze might get rather runny, I
shut everything off before ^10 softened. Unfortunately, shutting down when
^9 was bent prevented other glazes from maturing so I pretty much had a
lousy firing with much stuff having to be re fired and the rest hammered.
The recipe is as follows:
Custer Spar 5
Whiting 31
Tenn Ball Clay 24
Silica 22.5
Dolomite 2.5
Unwashed Wood Ash 15
RIO .75
Cobalt Carb .50
Rutile 4.0
I have never really worked with wood ash glaze recipes but really like the
look. Do any of you have any insight into what happened and how I could fix
the problem. I am wondering if I do away with the wood ash and replace it
with more calcium would I still have the same look without the grief. Any
suggestions or ideas.
Thanking you in advance and wishing everyone a Very Happy New Year.
--
Sincerely,
Ingeborg
www.thepottersworkshop.com
Lee on sat 29 dec 07
Hi Ingeborg,
Looking at the recipe and the tests on the page, this must
be a runny glaze. Often, with glazes like these, the test tile often
has a much thinner coat of glaze than when you glaze a full pot.
Did you scratch test both coats?
Try a thinner coat. Or try a much thinner coat on the
bottom half and a little thinner coat at the top half.
--
Lee in Mashiko, Tochigi Japan
http://mashikopots.blogspot.com/
"Tea is nought but this: first you heat the water, then you make the
tea. Then you drink it properly. That is all you need to know."
--Sen No Rikyu
"Let the beauty we love be what we do." - Rumi
Craig Martell on sat 29 dec 07
Hello Ingeborg:
I calculated the glaze as best I could without knowing what kind of ash you
are using and the type of ball clay too.
I did several calculations with different types ash and ball and the
results were not red hot any way that I did the analysis. The glaze is
very low in both alumina and silica and would probably have a tendency to
overfire and run. I would start with exchanging kaolin for the ball clay
and maybe just using all kaolin. Testing will tell. I would also look at
adding some feldspar and dropping the whiting. The KNaO is dismally low in
this glaze but since it seems to be based on the old Chinese Limestone/Clay
ash glazes we won't gripe too much about that. 31% whiting is a lot and
the wood ash will also add CaO.
You can try some tests with the above stuff or you can experiment with
glaze thickness to try and put the brakes on this stuff but factor in that
this glaze is so low in alumina and silica that it's not durable.
regards, Craig Martell Hopewell, Oregon
Ingeborg Foco on sat 29 dec 07
Hi Craig,
The ash came from my wood stove back in the Northwest (Camas, Wa to be
specific) When we moved, I had a bucket and moved it along with all of the
other studio stuff. Mostly as I recall we burned maple, doug fir, scrub
oak and 2x4 s which were mostly hemfir. Don't know know if that helps. I
use OM#4 ball clay.
I am disappointed to hear that you think this glaze is not very durable. I
guess I thought Van Guilder, a professional and a teacher, would not have a
glaze like that in his repertoire of functional work. Naturally all of my
test samples came out wonderful!!!. This is the height of the tourist
season and I don't know if I need the grief of another troublesome glaze; it
seems I have enough of those. I was just looking for another
color/dimension to add to my gallery offerings. I really like the rivulets
of ash glazes and thought I had it...ha. Is it really worth fiddling with
since it apparently has so many issues to overcome? I do like ash glazes
and especially like Richard ...can't now remember his name..OPA member used
to work at Georgies I have one of his mugs.,anyhow Is this glaze really
worth mucking about with? Can you steer me to something more workable?
Ingeborg
from Sunny and hot Florida where the temps are in the low 80's at the end of
December.
> I calculated the glaze as best I could without knowing what kind of ash
> you
> are using and the type of ball clay too.
>
> I did several calculations with different types ash and ball and the
> results were not red hot any way that I did the analysis. The glaze is
> very low in both alumina and silica and would probably have a tendency to
> overfire and run. I would start with exchanging kaolin for the ball clay
> and maybe just using all kaolin. Testing will tell. I would also look at
> adding some feldspar and dropping the whiting. The KNaO is dismally low
> in
> this glaze but since it seems to be based on the old Chinese
> Limestone/Clay
> ash glazes we won't gripe too much about that. 31% whiting is a lot and
> the wood ash will also add CaO.
>
> You can try some tests with the above stuff or you can experiment with
> glaze thickness to try and put the brakes on this stuff but factor in that
> this glaze is so low in alumina and silica that it's not durable.
>
> regards, Craig Martell Hopewell, Oregon
>
>
>
Ivor and Olive Lewis on sat 29 dec 07
Dear Ingeborg Foco,
<Reduction? It is published in John Britt's High fire Glaze book under =
Ash Glazes. >>
Custer Spar 5
Whiting 31
Tenn Ball Clay 24 =
Silica 22.5
Dolomite 2.5
Unwashed Wood Ash 15
RIO .75
Cobalt Carb .50
Rutile 4.0
It may be impossible to sort out this problem but perhaps the =
unreliability of your larger batch of material might be due to the =
nature of raw wood ash glaze. This will contain a large volume of Potash =
rich water. Potash is the principle melting agent in the recipe you =
give.
If you apply this to bisque ware the potash rich solution will soak into =
the porous fired clay and make no contribution to the bulk of the glaze. =
Furthermore, once Potash reaches its melting point it will commence =
reacting with silica, forming Potassium Silicate and discharge Carbon =
Dioxide. This would account for your cratering and blistering
Any discussion or description of using Raw Unwashed Ash as a glaze =
ingredient should address this aspect of the Science of glazing.
Applying a Raw Ash Glaze to leather hard clay would probable prevent the =
unwanted effects you describe.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Eva Gallagher on sat 29 dec 07
Hi Ingeborg
Try the fake ash glazes in Britt's book such as Hill Blue Ash as well as
Hannah Ash (got it from Clay Times I think). These are much more predictable
and do not seem to change if stored like real ash glzes do sometimes - but
still need spraying as will run if too thick.
Eva Gallagher
Deep River Ontario
----- Original Message -----
From: "Ingeborg Foco"
To:
Sent: Saturday, December 29, 2007 7:23 PM
Subject: Re: Van Gilder Wood Ash
> Hi Craig,
>
> The ash came from my wood stove back in the Northwest (Camas, Wa to be
> specific) When we moved, I had a bucket and moved it along with all of
> the
> other studio stuff. Mostly as I recall we burned maple, doug fir, scrub
> oak and 2x4 s which were mostly hemfir. Don't know know if that helps.
> I
> use OM#4 ball clay.
>
> I am disappointed to hear that you think this glaze is not very durable.
> I
> guess I thought Van Guilder, a professional and a teacher, would not have
> a
> glaze like that in his repertoire of functional work. Naturally all of my
> test samples came out wonderful!!!. This is the height of the tourist
> season and I don't know if I need the grief of another troublesome glaze;
> it
> seems I have enough of those. I was just looking for another
> color/dimension to add to my gallery offerings. I really like the
> rivulets
> of ash glazes and thought I had it...ha. Is it really worth fiddling with
> since it apparently has so many issues to overcome? I do like ash glazes
> and especially like Richard ...can't now remember his name..OPA member
> used
> to work at Georgies I have one of his mugs.,anyhow Is this glaze really
> worth mucking about with? Can you steer me to something more workable?
>
> Ingeborg
> from Sunny and hot Florida where the temps are in the low 80's at the end
> of
> December.
>
>
>
>
>> I calculated the glaze as best I could without knowing what kind of ash
>> you
>> are using and the type of ball clay too.
>>
>> I did several calculations with different types ash and ball and the
>> results were not red hot any way that I did the analysis. The glaze is
>> very low in both alumina and silica and would probably have a tendency to
>> overfire and run. I would start with exchanging kaolin for the ball clay
>> and maybe just using all kaolin. Testing will tell. I would also look
>> at
>> adding some feldspar and dropping the whiting. The KNaO is dismally low
>> in
>> this glaze but since it seems to be based on the old Chinese
>> Limestone/Clay
>> ash glazes we won't gripe too much about that. 31% whiting is a lot and
>> the wood ash will also add CaO.
>>
>> You can try some tests with the above stuff or you can experiment with
>> glaze thickness to try and put the brakes on this stuff but factor in
>> that
>> this glaze is so low in alumina and silica that it's not durable.
>>
>> regards, Craig Martell Hopewell, Oregon
>>
>>
>>
>
> ______________________________________________________________________________
> Clayart members may send postings to: clayart@lsv.ceramics.org
>
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots2@visi.com
>
>
Lee on sun 30 dec 07
On Dec 30, 2007 9:23 AM, Ingeborg Foco wrote:
>
> I am disappointed to hear that you think this glaze is not very durable. I
> guess I thought Van Guilder, a professional and a teacher, would not have a
> glaze like that in his repertoire of functional work.
Ingeborg,
You can't judge a potter by 3rd person recipes,
especially where natural materials are concerned. A professional
using natural materials like wood ash, knows you have to test the
glaze at least three times and adjust according to the results to get
the results you like.
As I mentioned previously, especially with wood
ash glazes, the primary differences between a small batch test and a
larger working batch is the thickness of application.
Thin test tiles pick up much less of the glaze than
the thickness of your average pot. The best determinate of glaze
thickness is scratching the surface and seeing the actual thickness.
--
Lee in Mashiko, Tochigi Japan
http://mashikopots.blogspot.com/
"Tea is nought but this: first you heat the water, then you make the
tea. Then you drink it properly. That is all you need to know."
--Sen No Rikyu
"Let the beauty we love be what we do." - Rumi
Bob Johnson on sun 30 dec 07
Ingegorg: I love ash glazes, too, and I realize that they are not the most stable, so I use them only on the outside of functional ware. But, because they have a disturbing tendency to run (which is why they can be beautiful), I always fire them on clay cookies. There is no need to avoid a less-than-stable glaze---just be careful where you use it.
Bob
--------------------------------------------------------
Robert L. Johnson
Psychoceramicist
106 Impala Drive
Roseburg, OR 97470
H: 541-672-5301
bjohnson@dcwisp.net
--------------------------------------------------------
Lee Love on mon 31 dec 07
On 12/31/07, Bob Johnson wrote:
> need to avoid a less-than-stable glaze---just be careful where you use it.
> Bob
Bob,
This are stable, if you know how to use them, as you mention.
I learned how to apply them during my apprenticeship and have
describe the method here previously. My teacher would thin his
Irabo glaze and apply the thinned glaze to the bottom half of the pot.
Then, he applied a thicker application to the top, but it was
thinner than your usual glaze. He almost always got perfect runs
stopping just before the foot.
Instead of thinning the glaze for the bottom of the pot,
I brush on the bottom part. Because the glaze moves, the brush marks
disappear.
I put up examples here:
http://mashikopots.blogspot.com/
--
Lee in Mashiko, Japan
http://groups.google.com/group/ClayCraft
"Men are born ignorant, not stupid. They are made stupid by
education." -- Bertrand Russell
Craig Martell on mon 31 dec 07
Ingeborg was saying:
>I am disappointed to hear that you think this glaze is not very durable.
Hello Ingeborg:
It's not as bad as all that. The glaze is low in alumina and silica so
it's not going to be as hard and resistant to acids as a glaze that has
more Al2O3 and SiO2 but it's not a dangerous or deadly concoction at
all. Unless, of course, someone loads this baby with colorants that can be
harmful if leached into your orange juice. So it goes.
How are you applying this glaze? Many, including meself, like to spray ash
glazes to control the thickness of application. These are "high flux"
glazes and usually need a thinner coat. You might try the glaze again by
spraying if you haven't already done that.
I've enclosed an adjustment to Bill's glaze and you might give it a try and
see if this moves things in the right direction while keeping the rivulet
thing happening. My revision is more durable but not in the accepted limit
range. I use some ash glazes that are very high in silica and are in the
ball park with alumina being ok but these aren't runners with rivulets.
When you bump up the Al2O3 and SiO2 past certain levels you don't get the
runs anymore.(pun intended) The ash glazes that I use which are not
runners are: celedons, chuns, and nukas.
So here's my revision. Let me know if you try this. I'll run some tests
thru the next kiln also.
Custer Spar 10.26
Whiting 21.15
Dolomite 1.73
Wood Ash 17.00
Epk 22.22
Silica 27.63
> I do like ash glazes and especially like Richard ...can't now remember
> his name..OPA member used
>to work at Georgies
I'll wager that you're talking about Ritchie Bellinger. Anyway, good luck
with the ash glazes and yes, they are worth working with and testing.
regards, Craig Martell Hopewell, Oregon
| |
|
