Bob Kavanagh on thu 26 sep 96
I've been working with earthenware the last few months, after not having
done so for many years. Right now I am firing to cone 02 and doing two
types of decoration: one with metallic slips for a burnt earth look and one
with glazes. My interest here is only the glazed ware. I have dipped
using tongs and large buckets (my normal habit);poured, using a jug simply
to pour the glazes over the pots (also a normal habit); and applied the
glaze on the wheel using a syringe and broad flat brush.
I bisque all ware to 04 in very slow, well ventilated bisque fires.
In both the dipping and pouring I am getting a fair amount of pin holing,
especially where the glaze is thick and almost not at all where the glaze
is thin.
In the cases where I brush on the glaze, there is absolutely no pin holing,
whether I apply the glaze very thickly, thickly or thinly.
It's not so much the pin holing itself which interests me ( I will work to
eliminate that) but rather that it does not occur when I brush on the glaze
(whether I apply it thickly or thinly and even on several occasions I have
brushed in on raw, fired it and had no pinholes).
Any ideas why?
I have been experimenting with "tile 1":
ferro frit 3124 - 64%
tile #6 - 12%
silica - 12%
talc - 4%
zinc oxide 4%
titania - 2%
bob kavanagh (60 km west of montreal)
Jeff Lawrence on sun 29 sep 96
Bob,
I am working with earthenware glazes, too, so your inquiry got my attention.
I entered your recipe in Insight (published by IMC, http:\\digitalfire.com)
to get an idea of the formula; I append its output. Your recipe shows two
suspicious characters on the pinhole front: zinc and titanium. According to
Insight's limit chart for leadless glazes at ^04-^02 (I stuck its numbers in
below), zinc should be 0-.2 -- yours is a little high. Maybe try reducing it
a bit?
Good luck!
Jeff
jml@roadrunner.com
505-753-5913 vox/fax
P.S. You might want to check out Insight for glaze testing. It makes a lot
of calculations easy that I never did before because (1) they were too hard
and (2) I'm lazy. I highly recommend the program (I have no affiliation with
IMC outside of being a satisfied customer).
<< INSIGHT OUTPUT -- EXCEPT FOR THINGS IN THESE BRACKETS >>
Tile 1 - Kavanagh
=================
FERRO FRIT 3124..... 64.00 74.42%
TILE #6 KAOLIN...... 12.00 13.95%
TALC................ 4.00 4.65%
ZINC OXIDE.......... 4.00 4.65%
TITANIUM DIOXIDE.... 2.00 2.33%
==========
86.00
FORMULA & ANALYSIS
==================
*CaO .52 10.75% << limit chart sez .1-.6 >>
*MgO .10 1.52% << limit chart sez 0-.2 >>
*K2O .01 .52% << limit chart sez 0-.5
*Na2O .21 4.75% for sum of K2O+Na2O >>
*ZnO .16 4.75% << limit chart sez 0-.2 >>
TiO2 .08 2.38%
B2O3 .41 10.48% << limit chart sez .3-1.1 >>
Al2O3 .35 13.17% << limit chart sez .1-.4 >>
SiO2 2.33 51.68% << limit chart sez 1.5-3 >>
COST/KG 1.88
RATIO 6.67
EXPAN 7.39
WEIGHT 270.44
Jeff Lawrence
Sun Dagger Design, Route 1 Box 394L, Espanola NM 87532
vox/fax: 505-753-5913
Lili Krakowski on sat 27 jun 09
Sharon sent in this 05-04 recipe which is not doing well with
cobalt in it. (Don't tell me! A BLUE glaze! Eeeeeek!) But it
is lovely with iron oxide (NOT blue!)
30.2 Gerstley Borate--
8.3 Lithium Carbonate
8.3 Nepheline Syenite
4 Kaolin--EPK
33.3 Flint
15.9 Whiting
100 Total
.264 Li2O
.065 Na2O
.01 K2O
.003 MgO
.658 CaO
1.000 Total
.129 Al2O3
.265 B2O3
.001 Fe2O3
1.765 SiO2
13.7 Ratio
68.8 Exp
(My recalculation from an over 1 k batch. Using GlazeMaster(tm) and
using their figure for 1999 GB)
Sharon uses yellow iron oxide
The lovely golden color reminded me--so I went back to Glaze
Master (dare not abbreviate it as GM!)
and found a glaze Bonnie Staffel gave me. Originally from Frank
Gaydos
Recipe Name: Bonnie Staffel Honey Glaze Frank Gaydos
30 Frit--Ferro 3124
26 Gerstley Borate--1999
20 Nepheline Syenite
10 Kaolin--EPK
10 Flint
4 Lithium Carbonate
100 Total
Additives
8 Iron Oxide--Red
Unity Oxide
.172 Li2O
.238 Na2O
.04 K2O
.003 MgO
.548 CaO
1.000 Total
.415 Al2O3
.496 B2O3
.002 Fe2O3
2.573 SiO2
6.2 Ratio
73.1 Exp
NB that the glaze that makes Sharon unhappy has a lot less
alumina and silica, too little, in fact, which. IMO always is a
distress call. I know Sharon says she only uses it on the
outside of pots--ah. well...and the hems of my sweat pants are
uneven, but I only wear them in the house!
So, Sharon, you can do blends and see how to modify the glaze you
have...or you can test the Staffel/Gaydos one, which I have used,
though not with cobalt.
As to cobalt. Colorants in glaze do their own thing. Some are
strong colorants, others weak, some are refractory, some are
fluxes. Some are neutral.
So what you have learned is that in that glaze cobalt--or the
amount of cobalt
you have, which is the maximum generally listed for cobalt
inclusion, and IMO well
above the "sensible"-- makes the glaze too refractory
Suggestion: make a blend and see if less colorant won't get you
what you want.
Suggestion: test the Staffel/Gaydos glaze and see if you get more
desirable results.
It also has more desirable COE.
Lili Krakowski
Be of good courage
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