David Beumee on wed 11 may 05
Ron and Jon,
Mastering Cone 6 Glazes talks about a silica level of 3.0 mols and an Alumina level of 0.25-0.45 mols for one particular set of fluxes for good stability of a base glaze at cone 6. What are your recommendations for silica and alumina levels for good stability/durability at cone 10? Are Si and Al levels dependant on the choice of fluxes or are there general guidelines you can give?
David Beumee
www.davidbeumee.com
Earth Alchemy Pottery
Lafayette, CO
-------------- Original message ----------------------
From: Ron Roy
> Hi Jon,
>
> No need to go that route - just institute a program of testing bodies and
> raw materials - you can then compensate for variable raw materials.
>
> Not rocket science - but it does take a particular point of view to start with.
>
> Not a bad idea to test glazes for stability either - then potters would
> know which are appropriate for liner glazes.
>
> RR
>
>
> >A ton of clay or a hundred pounds of glaze might get a bit expensive---but
> >hey!!--- I’m sure every potter will appreciate the stability of these
> >materials.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> ______________________________________________________________________________
> 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 11 may 05
Hi David,
While the experiments have not yet been done (they will get underway =20
later this year or early next), I speculate there will be little =20
difference--maybe none--at cone 10. After all glazes are used and leach =20=
(or not) at room (or oven) temperatures, not at their firing =20
temperature. therefore it should be their composition at room =20
temperature that is important. The primary difference in composition is =20=
the presence of boron and/or zinc at C6 where those materials are =20
rarely used at C10. I have not found them to be a big influence at C6 =20=
so I doubt their absence at C10 would have a big effect.
So far I have seen no significant effect of flux choice. That is what =20=
causes me to dislike 'Limit formulae'. When they are applied to fluxes =20=
all they seem to limit are your aesthetic options. About 1/2 the glazes =20=
in our book are outside traditional limits. And I can show you lots of =20=
glazes in the literature within limits that have awful stability. I =20
would point out that the literature says high levels of alkalis can =20
reduce stability. I have not explored that region yet--it may be so
The only place I would be a little cautious (and I have no large amount =20=
of data yet) would be with running up magnesium or barium to very high =20=
levels. They have limited solubility in a glaze melt and will =20
precipitate out (or never enter the melt) at fairly low levels =20
(compared to, say, calcium). This has the effect of lowering the flux =20=
content of the glaze or, said another way, running up the silica and =20
alumina levels to the point the glaze may not be well melted or may =20
devitrify on cooling. So I would recommend using no more of those =20
materials than is necessary to get a semimatte of matte surface. I =20
would avoid forcing them up into the dry matte region.
There is a lot of speculation in the above. It will be interesting to =20=
see if I have to eat my words in a year or so.
Regards,
John
On Wednesday, May 11, 2005, at 11:22 AM, David Beumee wrote:
> Ron and Jon,
> Mastering Cone 6 Glazes talks about a silica level of 3.0 mols and an =
=20
> Alumina level of 0.25-0.45 mols for one particular set of fluxes for =20=
> good stability of a base glaze at cone 6. What are your =20
> recommendations for silica and alumina levels for good =20
> stability/durability at cone 10? Are Si and Al levels dependant on the =
=20
> choice of fluxes or are there general guidelines you can give?
>
> David Beumee
> www.davidbeumee.com
> Earth Alchemy Pottery
> Lafayette, CO
>
>
>
>
>
>
>
>
>
>
> -------------- Original message ----------------------
> From: Ron Roy
>> Hi Jon,
>>
>> No need to go that route - just institute a program of testing bodies =
=20
>> and
>> raw materials - you can then compensate for variable raw materials.
>>
>> Not rocket science - but it does take a particular point of view to =20=
>> start with.
>>
>> Not a bad idea to test glazes for stability either - then potters =20
>> would
>> know which are appropriate for liner glazes.
>>
>> RR
>>
>>
>>> A ton of clay or a hundred pounds of glaze might get a bit =20
>>> expensive---but
>>> hey!!--- I=92m sure every potter will appreciate the stability of =
these
>>> materials.
>>
>> Ron Roy
>> RR#4
>> 15084 Little Lake Road
>> Brighton, Ontario
>> Canada
>> K0K 1H0
>> Phone: 613-475-9544
>> Fax: 613-475-3513
>>
>> =
______________________________________________________________________=20=
>> ________
>> 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 =20
>> melpots@pclink.com.
>
> =
_______________________________________________________________________=20=
> _______
> 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 =20
> melpots@pclink.com.
>
Craig Martell on thu 12 may 05
David asked:
>What are your recommendations for silica and alumina levels for good
>stability/durability at cone 10? Are Si and Al levels dependant on the
>choice of fluxes or are there general guidelines you can give?
Hello David:
If you have a glaze calculation program such as Matrix or Insight you can
find recommended levels of everything fluxes, alumina, silica, at any of
the usual temps we work at. Earthenware thru high fire. The recommended
limits will vary between authors but they're all pretty much in the ball
park for stable glass. You can also read Taylor and Bull, Parmelee, Van
Diver and Kingerey, and on and on it goes.
One of the tough things to do is figure out flux blends. This isn't
covered too heavily. There are lots of criteria about this such as color
influence, texture, expansion coefficients etc. If, for instance, a
potter wants to make a good, hard, stable dinnerware glaze the preceding
stuff applies but you're also concerned with durability and function of the
glaze over a long period of time. You want a very hard, non leacher, among
other things. I do line blends, triaxials, and quads of lots of different
fluxes. When I find the fluxes I want, at the mixture that gives the most
aggressive melt, I then load the glaze with alumina and silica. Silica is
my main concern after the flux mixture has been decided on. Silica, or
quartz, has a hardness of 7 out of 10 on Moh's scale. Knives and other
cutlery have a hardness of about 6.5 so they can't scratch quartz. But you
can't have a glaze that's 100% quartz so you have to be careful about the
blends. Orthoclase feldspar has a hardness of 6 so it would be a good
choice. Talc is not. Talc has a hardness value of 1. A good mineralogy
book can give you a lot of good information on just about everything a
potter uses.
For my time and money, the quickest and the most effective way to find some
very durable glazes along with getting a lot of other good info is to take
any of your flux blends and do a 35 glaze, Ian Currie, biaxial blend.
regards, Craig Martell Hopewell, Oregon
Ron Roy on thu 12 may 05
Hi David,
We don't know what the levels need to be - have not done the testing yet -
it is on the way.
It may be that the cone 6 levels will still be good at cone 10.
We did not come to any conclusions about the fluxes - high calcium is OK
obviously but we did not test high MgO or SrO - the zinc semi matte is
fairly high in ZnO and it's OK.
We did think about high sodium but never got the testing done for those.
So the answer is maybe, or we don't know yet.
I wouild guess - at this stage that keeping the silica between 4 and 5 and
the alumina .35 and .5 should do the trick - the glaze must be properly
melted though - putting in an opacifier may reverse the stability.
RR
>Ron and Jon,
> Mastering Cone 6 Glazes talks about a silica level of 3.0 mols and an
>Alumina level of 0.25-0.45 mols for one particular set of fluxes for good
>stability of a base glaze at cone 6. What are your recommendations for
>silica and alumina levels for good stability/durability at cone 10? Are Si
>and Al levels dependant on the choice of fluxes or are there general
>guidelines you can give?
>
>David Beumee
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Hesselberth on fri 13 may 05
On Friday, May 13, 2005, at 01:09 AM, Craig Martell wrote:
> The recommended
> limits will vary between authors but they're all pretty much in the
> ball
> park for stable glass.
Hi Craig,
I disagree with this statement. Traditional limit formulas have nothing
to do with stability of the glass. They were derived from examining
glazes that looked good. No data on stability was included in their
derivation. See the literature search I did on this subject several
years ago at
http://www.frogpondpottery.com/glazestab.html
Regards,
John
Craig Martell on fri 13 may 05
John was saying:
>I disagree with this statement. Traditional limit formulas have nothing
>to do with stability of the glass.
Hello John:
I wasn't talking about "traditional limit formulas". I was talking about
limit formula suggestions contained in most glaze calc computer
programs. The ones I've seen and used are fairly similar and give
suggestions for levels of materials that have a good probability of making
a stable glaze. What I meant by "authors", were authors of the computer
progarms. Looking back on this I can see why my comment could be easily
misunderstood. I should have said "program developer" or something similar.
To expand on this, my feeling now is that limit formula or any suggestion
of the correct mol equivalents for stable glass contained in any glaze at
any given temperature are mainly a guide to what might work. So those of
us who make our glazes will have to start somewhere in the ball park and
see to it that we make stable glass if that is our goal.
Thanks for you response to my post, Craig Martell Hopewell, Oregon
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