Jeff Lawrence on wed 29 sep 99
Hello Clayart,
I am writing to report on a glaze by Ron Roy that looks like it will work
very well for me.
My goal was to move away from my current production glaze, because
1.) it has frit 3289, a barium containing frit in it
2.) it has zinc oxide in it, which precludes firing glazed ware in my gas
kiln.
The ideal is a glaze that contains neither of the above noxins, is well
behaved as a slurry and submits readily to the addition of stains for
specific colors.
My first attempts were misdirected: I studied the Al:Si ratio of my glazes
and tried to get a high-alumina mat. I succeeded in making underfired
pinholey glazes that shivered like bikini models in the cold.
Ron took a different approach: for this temperature range, he said, better
to go with high calcium that will crystallize on cooling. This approach
means lower alumina, so as not to impede the calcium's crystal formation.
His first cut:
04RRA1 - zinc-free 04 base Rev A1 (04RRA1)
===========================================
FRIT 3134........... 35.00 31.25%
NEPHELINE SYENITE... 35.00 31.25%
WOLLASTONITE........ 25.00 22.32%
BENTONITE........... 2.00 1.79%
ZIRCOPAX............ 10.00 8.93%
EPK KAOLIN.......... 5.00 4.46%
========
112.00
CaO 0.71* 17.13%
MgO 0.01* 0.12%
K2O 0.04* 1.58%
Na2O 0.25* 6.60%
TiO2 0.00 0.03%
ZrO2 0.11 6.04%
Al2O3 0.22 9.73%
B2O3 0.24 7.27%
P2O5 0.00 0.01%
SiO2 1.97 51.22%
Fe2O3 0.00 0.24%
MnO 0.00* 0.02%
Si:Al 8.93
SiB:Al 10.03
Expan 8.40
The first tests were good glazes, well melted without running, but were for
my purposes too shiney, so over several trials we increased the calcium and
reduced the alumina further, arriving at RRA3:
Getting there -- making it more mat:
04RRA3 - zinc-free 04 base REV A3 (04RRA3)
===========================================
EPK KAOLIN.......... 4.46 4.46%
FRIT 3134........... 26.79 26.79%
NEPHELINE SYENITE... 26.79 26.79%
WOLLASTONITE........ 31.25 31.25%
BENTONITE........... 1.79 1.79%
ZIRCOPAX............ 8.93 8.93%
========
100.00
CaO 0.77* 20.48%
MgO 0.01* 0.15%
K2O 0.03* 1.37%
Na2O 0.19* 5.65%
TiO2 0.00 0.04%
ZrO2 0.10 6.04%
Al2O3 0.18 8.76%
B2O3 0.19 6.23%
P2O5 0.00 0.01%
SiO2 1.78 50.95%
Fe2O3 0.00 0.28%
MnO 0.00* 0.03%
Si:Al 9.87
SiB:Al 10.92
Expan 8.37
RRA3 looked good -- close to a flat mat -- but suffered from a nasty case
of the crawls. Dr. Roy diagnosed this as a function of low strength in the
dry glaze coating and recommended replacing the EPK (MOR of ~500) with OM4
(MOR of ~800)
Finally, I've got RRA3J, which includes the different clay, more calcium
and zircopax, and a little less alumina:
04RRA3J - zinc-free 04 base REV A3 (04RRA3j)
============================================
FRIT 3134........... 29.00 28.86%
NEPHELINE SYENITE... 23.00 22.89%
WOLLASTONITE........ 32.00 31.84%
BENTONITE........... 1.50 1.49%
ZIRCOPAX............ 10.00 9.95%
OM #4 BALL CLAY..... 5.00 4.98%
========
100.50
CaO 0.78* 21.21%
MgO 0.01* 0.17%
K2O 0.03* 1.20%
Na2O 0.18* 5.52%
TiO2 0.00 0.06%
ZrO2 0.11 6.75%
Al2O3 0.15 7.47%
B2O3 0.20 6.70%
SiO2 1.75 50.81%
Fe2O3 0.00 0.12%
Si:Al 11.55
SiB:Al 12.86
Expan 8.29
This glaze produces a not-quite-flat mat white and fires virtually
identically in gas and electric (except with iron-bearing colorants). It
takes the stains and oxides I've tried with good results
Mason 6600 - 8% for good black; 4% for charcoal gray
Mason 6650 6%/3%) - good black in gas and electric -- this is a cheaper
black that goes to russet in a zinc-containing glaze!
Mason 6221 - 6% for light turquoise
Gs-514 - good terra cotta in electric, muted in gas
Mason Fawn (6%/3%) yellow-tan
Copper carb (1%/.5%): turquoise electric and gas (unmixed chunks were moss
green)
Mason 6501 Silver Gray (6%/3%): pewter/light gray in gas and electric
Rutile (5%/2.5%): good mat tan possibility in electric; funky gray-green in
gas
Red Iron oxide (10%/5%): dry brown sandstone mat in electric;
bubble-textured coffee brown gloss in gas
This glaze is within Insight's limits, except for calcium, with no funky
materials in sight. The alumina and silica are right on the lower
boundaries. The glaze appears to fit well on my earthenware slip body (55%
clay and 45% talc) ... freeze-boil and all that are on the back burner -- I
don't use this on functional ware yet. I suspect it would be a pleasant
transparent mat without the zircopax, and will try that anon as well.
This has been an interesting and valuable exercise for me - I hope this
glaze is useful to others as well. Thank you, Ron Roy!
Best,
Jeff
Hank Murrow on thu 30 sep 99
>----------------------------Original message----------------------------
>Hello Clayart,
>
>I am writing to report on a glaze by Ron Roy that looks like it will work
>very well for me.
>
>My goal was to move away from my current production glaze, because
>1.) it has frit 3289, a barium containing frit in it
>2.) it has zinc oxide in it, which precludes firing glazed ware in my gas
>kiln...........Jeff
Good Morning Jeff; I was surprised to read your statement #2. I have been
firing many glazes containing Zinc in my lifting gas-fired kiln @ C/10 for
years and find Zinc a valuable collaborator. Why do you not use zinc?
Wondering, Hank in Eugene
Ron Roy on fri 1 oct 99
Zinc oxide is very easily reduced to the metal - which boils at low
temperature - the end result is that it is not there after reduction and so
it is not doing anything.
There is an excellent article in this months CM by David Hendley which is
to the point.
In gas kilns - even when used to fire in oxidation - it is difficult in
most cases to fire in complete oxidation - this leads to problems with
glazes that contain ZnO. When reading about ZnO there is usually the
comment - when it's there in more than minimum amounts - that it can lead
to pin hole problems. Even in electric kilns there is some reduction and
ZnO is very easy to reduce.
RR
>>----------------------------Original message----------------------------
>>Hello Clayart,
>>
>>I am writing to report on a glaze by Ron Roy that looks like it will work
>>very well for me.
>>
>>My goal was to move away from my current production glaze, because
>>1.) it has frit 3289, a barium containing frit in it
>>2.) it has zinc oxide in it, which precludes firing glazed ware in my gas
>>kiln...........Jeff
>
>Good Morning Jeff; I was surprised to read your statement #2. I have been
>firing many glazes containing Zinc in my lifting gas-fired kiln @ C/10 for
>years and find Zinc a valuable collaborator. Why do you not use zinc?
>Wondering, Hank in Eugene
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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