Anne Elisabeth Maurland on thu 14 jan 10
Hi Lili,
Let me start by saying that in general, I don't throw as thin as I used
to. Not just plates.
But you made me think of something.
There is one thing I do differently with the plates than with the rest
of the pots:
When I glaze my pots, I glaze the insides first, let them sit and dry
for several hours, and then I glaze the outsides. This is not practical
with plates, so I dunk them.
Is this what you mean by permeating the piece? If so, your theory may
be right, and throwing thicker may correct this, at least to some
extent.
I like plates better when they are thicker anyway.
I didn't do the freezing/boiling test with a plate, thinking it was
about fit between clay and glaze, so what difference would it make?
(And I didn't have any worthless plates sitting around.) But I will
now.
In general, I have always been happy with this glaze. It doesn't chip
or crackle, it doesn't settle much in the bucket, and I have never
noticed any variation in the results. To me, it's predictable. I also
think the pots hold up well, what with all the travelling, packing and
unpacking that I do at art fairs 12 times a year for 15 years. Of
course I have had many, many batches of the same clay body during that
time.
It was because of this particular customer, plus the plate problem,
that had me in an uproar.
I'm not sure what COE means, or the numbers you mention. I can't tell
any difference between my glaze and Ron's on the surface, and since I
can't (yet) find any real flaws in my own, I'm not sure I need to do
much more glaze searching. Perhaps you (or Ron) can convince me to do
his version. Actually, I probably will, to be sure.
Thank you for looking into this!
Elisabeth
On Jan 14, 2010, at 4:20 PM, lili krakowski wrote:
> This is theory and speculation.
>
> What do you think?
>
> I put both glazes --the original, and RR's Revise (RRR) through
> GlazeMaster (TM) and got that the original had 57 some COE, and RRR
> 65/69 depending on GB origin.
>
> Original:
>
>> 50 gerstley borate
>> 15 Kaolin
>> 35 Silica
>
>
> .111 Na2O
> .003 K2O
> .002 MgO
> .884 CaO
> 1.000 Total
>
> .422 Al2O3
> .87 B2O3
> .003 Fe2O3
>
> 3.956 SiO2
> .9.4 Ratio
> 57.3 Exp
>
>
> The RR revision goes like this:
>
> 46 Gerstley Borate--9/97
> 10 Kaolin--EPK
> 22 Silica
> 22 Feldspar--G-200
>
> .174 Na2O
> .099 K2O
> .153 MgO
> .573 CaO
> 1.000 Total
>
> .315 Al2O3
> .713 B2O3
> .006 Fe2O3
>
> 2.908 SiO2
>
>
> 69.6 Exp
>
> BUT if you use GB from '99 the Exp is only around 65.
>
> Now I personally HATE Gerstley Borate for a number of reasons: that
> depending on source and time and like that it varies; and also because
> it is somewhat water soluble, to which I will return.
>
> Then I doodled with it some more and got:
>
>
> 58.4 Frit--Ferro 3195
> 10 Bentonite
> 19.6 Silica
> 12.1 Whiting
>
>
>
> .206 Na2O
> .002 K2O
> .028 MgO
> .764 CaO
> 1.000 Total
>
> .289 Al2O3
> .645 B2O3
> 2.876 SiO2
>
> 68.1 Exp
>
> What I like is that whiting shrinks a lot, and therefore gives you
> some "space" to play with.
>
> This is a calcium borate glaze of which there are many. You may end
> up happier with another recipe altogether.
>
> BUT here comes a theory I cannot really test, but your saying you
> throw very thin brings chills to my heart.
>
> My theory is this--and PLEASE everyone shoot it down--that when water
> soluble materials are used, they seep into the body....If a pot is
> very thin, then the soluble material permetates the WHOLE body of the
> pot, fluxing it, in essence, and making it much weaker, more fragile.
>
> One of my opinionated opinions is that it it neither the glaze, NOR
> the body that determines things, but the interface of the two. The
> soluble materials affect that interface a whole lot.
>
> Now Elizabeth. I find it very hard to believe that someone bought
> functional pottery and never used it...Even if she planned to use it
> for Passover tableware, a year includes one Passover...And if she
> displayed the pieces she may not have USED them, but may have washed
> them here and there.
>
> You write that a few of your plates broke, so you now make thicker
> plates.
> That may be "where it is at." That the ware is too thin to sustain
> that glaze.
>
> And last--are you using the same batch of clay as you have been using
> all along? Or did a new supply of "same" body get in the production
> cycle there somewhere?
>
> I wish you the best.
>
> Lili Krakowski
> Be of good courage
>
>
>
lili krakowski on thu 14 jan 10
This is theory and speculation.
What do you think?
I put both glazes --the original, and RR's Revise (RRR) through =3D
GlazeMaster (TM) and got that the original had 57 some COE, and RRR =3D
65/69 depending on GB origin. =3D20
Original:
> 50 gerstley borate
> 15 Kaolin=3D20
> 35 Silica
.111 Na2O
.003 K2O
.002 MgO
.884 CaO
1.000 Total
.422 Al2O3
.87 B2O3
.003 Fe2O3
3.956 SiO2
.9.4 Ratio
57.3 Exp
The RR revision goes like this:
46 Gerstley Borate--9/97
10 Kaolin--EPK
22 Silica
22 Feldspar--G-200
.174 Na2O
.099 K2O
.153 MgO
.573 CaO
1.000 Total
.315 Al2O3
.713 B2O3
.006 Fe2O3
2.908 SiO2
69.6 Exp=3D20
BUT if you use GB from '99 the Exp is only around 65.
Now I personally HATE Gerstley Borate for a number of reasons: that =3D
depending on source and time and like that it varies; and also because =3D
it is somewhat water soluble, to which I will return.
Then I doodled with it some more and got:
=3D20
=3D20
58.4 Frit--Ferro 3195
10 Bentonite
19.6 Silica
12.1 Whiting
=3D20
=3D20
.206 Na2O
.002 K2O
.028 MgO
.764 CaO
1.000 Total
.289 Al2O3
.645 B2O3
2.876 SiO2
68.1 Exp
What I like is that whiting shrinks a lot, and therefore gives you some =
=3D
"space" to play with. =3D20
This is a calcium borate glaze of which there are many. You may end up =3D
happier with another recipe altogether.
BUT here comes a theory I cannot really test, but your saying you throw =3D
very thin brings chills to my heart.
My theory is this--and PLEASE everyone shoot it down--that when water =3D
soluble materials are used, they seep into the body....If a pot is very =
=3D
thin, then the soluble material permetates the WHOLE body of the pot, =3D
fluxing it, in essence, and making it much weaker, more fragile.
One of my opinionated opinions is that it it neither the glaze, NOR the =3D
body that determines things, but the interface of the two. The soluble =3D
materials affect that interface a whole lot.
Now Elizabeth. I find it very hard to believe that someone bought =3D
functional pottery and never used it...Even if she planned to use it for =
=3D
Passover tableware, a year includes one Passover...And if she displayed =3D
the pieces she may not have USED them, but may have washed them here and =
=3D
there.
You write that a few of your plates broke, so you now make thicker =3D
plates.
That may be "where it is at." That the ware is too thin to sustain that =
=3D
glaze.
And last--are you using the same batch of clay as you have been using =3D
all along? Or did a new supply of "same" body get in the production =3D
cycle there somewhere?
I wish you the best.
Lili Krakowski
Be of good courage
=3D20
| |
|
