Dave Finkelnburg on sat 22 jul 06
Danger, Will Roginson! I'm about to launch into a
rant...about why you want to calculate glazes if you
want to make heads or tails of them. Here's what's on
my mind.
Ivy posted a glaze, Ivor offered some correct
comments on the glaze. What does the reader learn
from these two posts?
Not nearly as much as comes from a quick run of the
glaze recipe through a glaze calculation program...in
my case, Glazemaster by John Hesselberth. The result
shows, in moles:
0.53 Na2O, 0.9 K2O, .38 Cao, .34 Al2O3, 2.6 SiO2. In
weight%: 12 Na2O, 3 K2O, 7.6 CaO, 12 Al2O3, 55 SiO2.
It also shows the glaze is very high in coefficient of
thermal expansion so it will craze on virtually
everything!
What does this mean? Simply, this is a balanced
high-alkaline glaze, glossy when properly fired,
containing adequate alumina and silica to make a
physically durable glaze...and a glaze that, despite
it's high sodium content, will probably be underfired
at cone 04. On that point one needs a report from
someone who has made that test or one needs to make
their own test. Testing has shown the 7.7% copper
oxide content means the glaze won't be chemically
durable...it will leach copper in some conditions.
The point is, a recipe is a very difficult to
analyze. But, reduce the recipe to a chemical formula
by using the chemical contents of the raw materials
and you can quickly see important patterns that tell
you much about the glaze.
Does this information tell you whether to use the
glaze? Of course not. Only you know what you want.
It does, though, tell you ABOUT the glaze...and that
empowers you to spend less time on trial and error and
more on purposeful glaze exploration.
Good glazing!
Dave Finkelnburg
PS: I figured soda spar in my calculation above, a
different spar will change the result...
PPS: The glaze will be hard to use...soda ash is
soluble, there's no clay to keep the glaze
suspended...
PPPS: While I used Glazemaster, at least a dozen
other programs out there will also calculate glazes.
Glazemaster is working well for me, and it's VERY
affordable, only $50US at
http://www.frogpondpottery.com/
--- Ivor and Olive Lewis
wrote:
> Dear Ivy,
>
> You ask and suggest <<...For this round, I have
> acquired a very "mysterious" secret formula for an
> Egyptian Blue glaze that was used commercially in
> the 20's and 30's by a prominent art pottery.
> Formula looks kinda weird to me, but, the photos are
> beautiful,
> Here it is as it came to me:
> Egyptian Blue
> Soda ash 62
> Whiting 21
> Feldspar 111
> Silica 24
> Add Copper Oxide 18
> I believe it is supposed to be a cone 04
> formula.0..>>
>
> An interesting Composition but not one that would be
> considered to be durable as a surface coating for a
> clay object, if indeed it can be regarded as a
> "Glaze". Since it contains a soluble component it
> will be difficult to manage. If applied to a porous
> bisque pot the soluble material will be drawn into
> the clay by capillary action. This will reduce the
> chances that it will fuse to form a cohesive
> vitreous finish. The percentage of copper oxide
> means that it might only be used for decoration and
> therefore would have no utilitarian function.
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Liisa Reid on sat 22 jul 06
OK, now I'm really confused, by two very different calculations
of the Egyptian Blue "mystery" glaze.
Is there an error somewhere, or how can a recipe using such
basic ingredients be so different depending on what program
is used for the calculations? Thanks for any enlightenment.
Regards,
Liisa Reid, clayart junkie and occasional poster
On Jul 22, 2006, at 1:01 PM, Dave Finkelnburg wrote:
> Ivy posted a glaze, Ivor offered some correct
> comments on the glaze. What does the reader learn
> from these two posts?
> Not nearly as much as comes from a quick run of the
> glaze recipe through a glaze calculation program...in
> my case, Glazemaster by John Hesselberth. The result
> shows, in moles:
> 0.53 Na2O, 0.9 K2O, .38 Cao, .34 Al2O3, 2.6 SiO2. In
> weight%: 12 Na2O, 3 K2O, 7.6 CaO, 12 Al2O3, 55 SiO2.
I've checked it in Glazemaster and got the same result, posted
below in Glazemaster format. Ron Roy's calculation follows.
Recipe Name: Egyptian Blue (calculation with Glazemaster)
Cone: Color:
Firing: Surface:
Amount Ingredient
62 Soda Ash
21 Whiting
111 Feldspar--G-200
24 Silica
218 Total
Unity Oxide
.437 Na2O
.203 K2O
.002 MgO
.358 CaO
1.000 Total
.324 Al2O3
.001 Fe2O3
2.636 SiO2
8.1 Ratio
106.3 Exp
Comments:
-----------------------------------
Calculations by GlazeMaster=99
www.masteringglazes.com
------------------------------------
On Jul 22, 2006, at 3:49 PM, Ron Roy wrote:
> Untitled Recipe 2
> -----------------
> SODA ASH............ 62.00
> WHITING............. 21.00
> G 200 SPAR.......... 111.00
> SILICA.............. 24.00
> ----------
> 218.00
> FORMULA & ANALYSIS
> ------------------
> *CaO........ .22
> *MgO........ .00
> *K2O........ .13
> *Na2O....... .65
> Fe2O3...... .00
> AL2O3...... .20
> SiO2....... 1.66
>
> RATIO 8.16
> EXPAN 1308.78
> WEIGHT 184.97
>
> Copper not included - not stable - and going to craze badly.
>
> RR
Ron Roy on sun 23 jul 06
Hi Lisa,
You have the answer in this case - you will find that the calculation
programs are all using the same way to calculate - there will always be
some small differences because of the different rounding off used by
different authors, different analysis and sometimes just plain old errors
in analysis.
It is always wise to get "good" analysis and make sure they represent a
close approximation of the materials you are using.
There was a program that did not take into account LOI that I ran across
many years ago. That would certainly produce large errors. Calcium
Carbonate has a LOI of about 45% - so any calculation that did not take
that into account would indicate there was a lot more whiting than there
actually was.
I have been using calculation programs for many years now - they work - as
Dave explained in his rant - if you want to understand what is going on -
one of the most important tools is calculation.
RR
>OK, now I'm really confused, by two very different calculations
>of the Egyptian Blue "mystery" glaze.
>
>Is there an error somewhere, or how can a recipe using such
>basic ingredients be so different depending on what program
>is used for the calculations? Thanks for any enlightenment.
>
>Regards,
>Liisa Reid, clayart junkie and occasional poster
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Liisa Reid on sun 23 jul 06
Ron,
I admire and respect both yours and John Hesselberth's
contributions to the list. Hence my confusion.
I used the default value for soda ash in Glazemaster v2.3.
So now, I've gone to digital fire's materials database and
found the same result for "soda ash". But there is also a
listing for "hydrous sodium carbonate" that gives the result that
you got. Does this mean that "soda ash" in a recipe should be
understood to mean "hydrous sodium carbonate"?
Liisa Reid
Struggling to get meaningful results out of glaze calculation
On Jul 23, 2006, at 12:08 PM, Ron Roy wrote:
> Hi Lisa,
>
> You have the answer in this case - you will find that the calculation
> programs are all using the same way to calculate - there will
> always be
> some small differences because of the different rounding off used by
> different authors, different analysis and sometimes just plain old
> errors
> in analysis.
>
> It is always wise to get "good" analysis and make sure they
> represent a
> close approximation of the materials you are using.
>
> There was a program that did not take into account LOI that I ran
> across
> many years ago. That would certainly produce large errors. Calcium
> Carbonate has a LOI of about 45% - so any calculation that did not
> take
> that into account would indicate there was a lot more whiting than
> there
> actually was.
>
> I have been using calculation programs for many years now - they
> work - as
> Dave explained in his rant - if you want to understand what is
> going on -
> one of the most important tools is calculation.
>
> RR
>
>> OK, now I'm really confused, by two very different calculations
>> of the Egyptian Blue "mystery" glaze.
>>
>> Is there an error somewhere, or how can a recipe using such
>> basic ingredients be so different depending on what program
>> is used for the calculations? Thanks for any enlightenment.
>>
>> Regards,
>> Liisa Reid, clayart junkie and occasional poster
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
>
> ______________________________________________________________________
> ________
> 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.
Liisa Reid on sun 23 jul 06
Ron,
Got it figured out!
My mistake looking up the values for
soda ash (anhydrous sodium carbonate) and
hydrous sodium carbonate at digital fire.
I got my eyes crossed.
Which makes Ron's calculation correct and I
need to update my copy of glazemaster v2.3
with the corrected value, which should be
Na2O 58.49
CO2 (LOI) 41.51
Thanks to Dave Finkelnburg for unraveling my
confusion.
Liisa
On Jul 23, 2006, at 4:45 PM, Liisa Reid wrote:
> Ron,
> I admire and respect both yours and John Hesselberth's
> contributions to the list. Hence my confusion.
>
> I used the default value for soda ash in Glazemaster v2.3.
> So now, I've gone to digital fire's materials database and
> found the same result for "soda ash". But there is also a
> listing for "hydrous sodium carbonate" that gives the result that
> you got. Does this mean that "soda ash" in a recipe should be
> understood to mean "hydrous sodium carbonate"?
>
> Liisa Reid
> Struggling to get meaningful results out of glaze calculation
>
>
>
>
> On Jul 23, 2006, at 12:08 PM, Ron Roy wrote:
>
>> Hi Lisa,
>>
>> You have the answer in this case - you will find that the calculation
>> programs are all using the same way to calculate - there will
>> always be
>> some small differences because of the different rounding off used by
>> different authors, different analysis and sometimes just plain old
>> errors
>> in analysis.
>>
>> It is always wise to get "good" analysis and make sure they
>> represent a
>> close approximation of the materials you are using.
>>
>> There was a program that did not take into account LOI that I ran
>> across
>> many years ago. That would certainly produce large errors. Calcium
>> Carbonate has a LOI of about 45% - so any calculation that did not
>> take
>> that into account would indicate there was a lot more whiting than
>> there
>> actually was.
>>
>> I have been using calculation programs for many years now - they
>> work - as
>> Dave explained in his rant - if you want to understand what is
>> going on -
>> one of the most important tools is calculation.
>>
>> RR
>>
>>> OK, now I'm really confused, by two very different calculations
>>> of the Egyptian Blue "mystery" glaze.
>>>
>>> Is there an error somewhere, or how can a recipe using such
>>> basic ingredients be so different depending on what program
>>> is used for the calculations? Thanks for any enlightenment.
>>>
>>> Regards,
>>> Liisa Reid, clayart junkie and occasional poster
>>
>> Ron Roy
>> RR#4
>> 15084 Little Lake Road
>> Brighton, Ontario
>> Canada
>> K0K 1H0
>>
>> _____________________________________________________________________
>> _
>> ________
>> 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.
>
> ______________________________________________________________________
> ________
> 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.
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