Al Sather on thu 13 jan 00
I have started developing a glaze for some dinnerware.
Spodumene 51.0 %
Talc 43.0 %
Frit 3134 2.0 %
Bentonite 2.0 %
Magnesium Carbonate 2.0 %
Plus Iron dust 2.0 %
or Iron dust 4.0 % (for trim)
The "iron dust" is collected from a old shipping port
when iron ore was loaded.
I get a nice cream colored glaze with nice texture and
some iron flecking. At 4%, the trim, used or the rim,
is darker, and very textured. While I like that texture
some people may find it rough.
My question, does this glaze appear to have any potential
leaching problems, or other major flaws.
Thank you for any comments that you may have.
Al Sather
Dogberry Clay Studio
PO 189, RR #1
Paradise, NF A1L 1C1
Stephen Grimmer on fri 14 jan 00
Al,
I'm assuming you fire this glaze to cone 10 in reduction. As this glaze
stands, it is rather under supplied with both silica and alumina. There may
be durability issues because of this. The calculated expansion is very low,
but because of the over supply of lithium, calculated expansion should be
considered an unreliable predictor of glaze behavior. The glaze is also over
supplied with magnesium.
As far as safe use on food contact surfaces goes, there are some who
feel that lithium-bearing glazes should not be used due to the high numbers
of the population who are on lithium therapy. I haven't seen any numbers on
lithium release in glazes, so I can't comment. I can say that I use high
lithium shino glazes in cups and on plates, even though they break all sorts
of 'rules' on glaze formulation. Iron is considered a safe colorant in just
about all cases, so I wouldn't worry about that.
I've brought the silica up to within normal limits, and left the flux
oxides the same to preserve the color response somewhat. The addition of EPK
should help keep the glaze suspended in the bucket better, too. Still, I'm
not really comfortable with recommending this glaze anyway, what with the
magnesium and lithium so high like that.
Two Recipes: Al's Yellow 1 & Untitled Recipe 1
==================================================
SPODUMENE........... 51.00 49.04% 38.48 37.00%
TALC................ 43.00 41.35% 32.44 31.19%
FRIT 3134........... 2.00 1.92% 1.51 1.45%
MAGNESIUM CARBONATE. 2.00 1.92% 1.51 1.45%
BENTOLITE L......... 2.00 1.92% 1.51 1.45%
Fe2O3............... 4.00 3.85% 4.00 3.85%
FLINT............... 14.51 13.95%
EPK KAOLIN.......... 10.05 9.66%
======== ========
104.00 104.00
CaO 0.02* 0.46% 0.04* 0.88%
Li2O 0.24* 3.80% 0.23* 2.91%
MgO 0.69* 15.00% 0.66* 11.49%
K2O 0.00* 0.06% 0.00* 0.08%
Na2O 0.01* 0.36% 0.01* 0.28%
SrO 0.00* 0.00% 0.00* 0.00%
TiO2 0.00 0.01% 0.00 0.05%
Al2O3 0.24 13.30% 0.32 13.95%
B2O3 0.01 0.45% 0.01 0.35%
P2O5 0.00 0.02%
SiO2 1.93 62.58% 2.56 65.91%
Fe2O3 0.05* 3.96% 0.06* 4.09%
Cost/kg 0.33 0.39
Si:Al 7.98 8.02
SiB:Al 8.03 8.05
Expan 4.42 4.48
This next one is a recalculation of MG-2, a longtime favorite magnesium base
that Marguerite Wildenhain used to use. I've modified it to source the boron
from frit 3434 instead of Gerstley borate. The glaze is just a bit low in
silica and a bit high in magnesium. I don't know how big a deal that is,
really. Maybe others can address that. Additions of iron should give you
some nice yellows.
MG-2 revised.
=================
FLINT............... 15.31 15.31%
F-4 FELDSPAR........ 17.50 17.50%
TALC................ 19.43 19.43%
EPK KAOLIN.......... 19.40 19.40%
FRIT 3134........... 28.36 28.36%
========
100.00
CaO 0.33* 6.79%
MgO 0.45* 6.75%
K2O 0.03* 0.93%
Na2O 0.19* 4.28%
TiO2 0.00 0.07%
Al2O3 0.30 11.12%
B2O3 0.26 6.77%
P2O5 0.00 0.05%
SiO2 2.85 63.07%
Fe2O3 0.00* 0.17%
Cost/kg 1.75
Si:Al 9.63
SiB:Al 10.52
Expan 6.29
--
Steve Grimmer
Bowling Green State University
Bowling Green, OH
----------
>From: Al Sather
>To: CLAYART@LSV.UKY.EDU
>Subject: Looking for comments on a lithium glaze
>Date: Thu, Jan 13, 2000, 3:37 PM
>
> ----------------------------Original message----------------------------
> I have started developing a glaze for some dinnerware.
>
> Spodumene 51.0 %
> Talc 43.0 %
> Frit 3134 2.0 %
> Bentonite 2.0 %
> Magnesium Carbonate 2.0 %
>
> Plus Iron dust 2.0 %
> or Iron dust 4.0 % (for trim)
>
>
> The "iron dust" is collected from a old shipping port
> when iron ore was loaded.
>
> I get a nice cream colored glaze with nice texture and
> some iron flecking. At 4%, the trim, used or the rim,
> is darker, and very textured. While I like that texture
> some people may find it rough.
>
> My question, does this glaze appear to have any potential
> leaching problems, or other major flaws.
>
> Thank you for any comments that you may have.
>
> Al Sather
> Dogberry Clay Studio
> PO 189, RR #1
> Paradise, NF A1L 1C1
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