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## coefficient of expansion! a plea for calculation !

### Lili Krakowski on sat 13 aug 11

It is quite wonderful when someone makes your point for you!

In our last installment, comments were made that newcomers to glaze =3D
should do the reading, LEARN the mechanics--or do I mean dynamics? ( =3D
never sure) of what's what with glaze., and test.

Now comes a question: If the glaze discussed has too low a coefficient =3D
of expansion, what does one do?

Once more, with feeling. You look at the materials, and, knowing what =3D
they are, and what they do, test. But glaze calculation saves you time =3D
and money.

The question originally posed was how to color this clear glaze:

Silica 25 %
Kaolin 15
Talc 10
Gerstley Borate 25
Nepheline Syenite 25

whose molecular analysis is

.214 Na2O
.053 K2O
.311 MgO
.423 CaO
1.000 Total

.535 Al2O3
.38 B2O3
.004 Fe2O3

3.966 SiO2

61.9 Exp

And as Frans Wildenhain would say (and us fortunates who were his =3D
students still say: "What do I see here with my eyes?")-- a COE of 61.9! =
=3D
And RonJohn warn us not to get the COE below 65. Which Ron reiterated =3D

What accounts for that? Materials that do not shrink. Immensely =3D
simplified, but so.=3D20

What can you do?

Reduce the amount of silica.

Reducing the silica to 15 gives this:

.214 Na2O
.053 K2O
.311 MgO
.423 CaO

.535 Al2O3
.38 B2O3
.004 Fe2O3

3.282 SiO2

65.2 Exp

Calculations by GlazeMasterT

Still a good sufficiency of silica. But higher COE.

And yes I could have done it with pencil, paper, slide rule or =3D
calculator...

By the way. I would not use that glaze a a clear over underglaze or =3D
slips...--as the magnesium will affect colors. It may be form lovely =3D
opaque creamy glaze that can be colored attractively on its own.

Lili Krakowski
Be of good courage

### Jean Eiers-Page on sun 14 aug 11

Hi Lil,

If you are reducing the silica from 25 to 15% - then what are you =3D
increasing?

This is a cone 6 ox. glaze.

Jean

On 2011-08-13, at 4:50 PM, Lili Krakowski wrote:

> It is quite wonderful when someone makes your point for you!
>=3D20
> In our last installment, comments were made that newcomers to glaze =3D
should do the reading, LEARN the mechanics--or do I mean dynamics? ( =3D
never sure) of what's what with glaze., and test.
>=3D20
> Now comes a question: If the glaze discussed has too low a coefficient =
=3D
of expansion, what does one do?
>=3D20
> Once more, with feeling. You look at the materials, and, knowing what =
=3D
they are, and what they do, test. But glaze calculation saves you time =3D
and money.
>=3D20
> The question originally posed was how to color this clear glaze:
>=3D20
> Silica 25 %
> Kaolin 15
> Talc 10
> Gerstley Borate 25
> Nepheline Syenite 25
>=3D20
> whose molecular analysis is
>=3D20
> .214 Na2O
> .053 K2O
> .311 MgO
> .423 CaO
> 1.000 Total
>=3D20
> .535 Al2O3
> .38 B2O3
> .004 Fe2O3
>=3D20
> 3.966 SiO2
>=3D20
> 61.9 Exp
>=3D20
>=3D20
>=3D20
> And as Frans Wildenhain would say (and us fortunates who were his =3D
students still say: "What do I see here with my eyes?")-- a COE of 61.9! =
=3D
And RonJohn warn us not to get the COE below 65. Which Ron reiterated =3D
>=3D20
> What accounts for that? Materials that do not shrink. Immensely =3D
simplified, but so.=3D20
>=3D20
> What can you do?
>=3D20
>=3D20
>=3D20
> Reduce the amount of silica.
>=3D20
> Reducing the silica to 15 gives this:
>=3D20
>=3D20
> .214 Na2O
> .053 K2O
> .311 MgO
> .423 CaO
>=3D20
> .535 Al2O3
> .38 B2O3
> .004 Fe2O3
>=3D20
> 3.282 SiO2
>=3D20
> 65.2 Exp
>=3D20
> Calculations by GlazeMasterT
>=3D20
> Still a good sufficiency of silica. But higher COE.
>=3D20
> And yes I could have done it with pencil, paper, slide rule or =3D
calculator...
>=3D20
> By the way. I would not use that glaze a a clear over underglaze or =3D
slips...--as the magnesium will affect colors. It may be form lovely =3D
opaque creamy glaze that can be colored attractively on its own.
>=3D20
>=3D20
>=3D20
>=3D20
>=3D20
>=3D20
> Lili Krakowski
> Be of good courage
>=3D20