Ivor and Olive Lewis on sat 22 jul 06
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.
I would be interested in the results from a Computer analysis. Perhaps =
John or Ron would oblige.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivy Glasgow on sat 22 jul 06
On Sat, 22 Jul 2006 14:49:03 -0500, 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
Thanks for confirming my suspicions. If I was bound and
determined to mess around with this formula, would there be any
point in revising the recipe to contain more alumina and
silica? I wonder if that would stabilize the glaze,
or would it also ruin the luscious color response?
I suppose it won't hurt to mix up a few hundred
grams of this and that and see what the fire returns.
-Ivy G.
Ivy Glasgow on sat 22 jul 06
>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.>>
>
>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.
>
>I would be interested in the results from a Computer analysis. Perhaps John
or Ron would oblige.
>
Here is the unity formula as calculated in GlazeChem.
Na2O 0.53 Al2O3 0.16 SiO2 1.39
K2O 0.10 Fe2O3 0.00
CaO 0.18
CuO 0.19
Alumina:Silica ratio is 1.00:8.86
Neutral:Acid ratio is 1.00:8.87
Alk:Neut:Acid ratio is 1.00:0.16:1.40
Expansion: 134.5 x 10e-7 per degree C
I am guessing that the 18% copper may be a typo. At any rate when I test it
I will start with 3% and work up from there.
I tried to recalculate the materials with materials that aren't water
soluble but couldn't find anything to provide that much sodium without
providing too much of something else.
-Ivy G.
Ron Roy on sat 22 jul 06
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
>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.
>
>I would be interested in the results from a Computer analysis. Perhaps
>John or Ron would oblige.
>
>Best regards,
>
>Ivor Lewis.
>Redhill,
>South Australia.
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on sun 23 jul 06
Dear Ivy Glasgow ,
Thank you for that information.
Those values confirm my suspicions that this is a highly unstable =
material.
It is not commonplace to include colouring agents in the Seger =
calculation. When you remove Copper oxide from the R2O column it makes =
things look far worse. I would imagine this stuff will craze and also be =
water soluble. Others may have a different opinion
Best regards,
Ivor
Ron Roy on sun 23 jul 06
Hi Ivy,
If you added 20 EPK and another 45 silica you would be at the lower end of
stability for a cone 6 glaze - the copper is at 7.6% in your original
recipe - way too much to stay in a glaze as it cools - so some will be
right on the surface.
Copper is the hardest colour to keep in a glaze - so even this revised
glaze will leach copper - even with a small amount of copper - and it will
be still be crazed - which exposes even more surface to any acidic food to
work on.
Coupled with all that - as Ivor pointed out - the soda ash is soluble - so
sodium is going to migrate during drying - and sodium will be deposited in
different amounts on the ware.
Sounds like a loosing proposition to me - as a liner glaze.
I suggest you start with Ferro Frit 3110 - it has lots of sodium and is
only sightly soluble in water - I have lost track of what cone you want to
fire it at - I think it was quite low - so try this and vary the amount of
EPK up and down a bit - and protect your shelves.
I don't think it will be stable as a liner glaze - just too much sodium -
but testing will tell - and keep the copper Carb. down to 1 or 2% - that
will be enough to get good colour.
Frit 3110 - 80.0
EPK - 20.0
Bentonite - 2.0
Total 102.0
It will still craze - I tried adding silica and there is no point - I got
up to 50 more silica and the expansion is still high.
RR
>On Sat, 22 Jul 2006 14:49:03 -0500, 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
>
>Thanks for confirming my suspicions. If I was bound and
>determined to mess around with this formula, would there be any
>point in revising the recipe to contain more alumina and
>silica? I wonder if that would stabilize the glaze,
>or would it also ruin the luscious color response?
>
>I suppose it won't hurt to mix up a few hundred
>grams of this and that and see what the fire returns.
>-Ivy G.
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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