Cindy Strnad on sat 17 mar 01
Hi, Guys.
Well, I just unloaded a bunch of cool glaze tests, so I thought I'd share
them with you. The first group of tests were done using the Opal Blue base,
which follows:
EPK KAOLIN.......... 25.00 25.00%
FRIT 3134........... 50.00 50.00%
SILICA.............. 25.00 25.00%
========
100.00
CaO 0.68* 10.46%
MgO 0.00* 0.03%
K2O 0.00* 0.09%
Na2O 0.31* 5.35%
TiO2 0.00 0.10%
Al2O3 0.35 9.78%
B2O3 0.63 11.97%
P2O5 0.00 0.06%
SiO2 3.76 61.96%
Fe2O3 0.00 0.21%
Cost/kg 2.49
Si:Al 10.75
SiB:Al 12.54
Expan 6.84
These figures are the standard figures in the Material Data Table provided
with Insight.
Normally, I'd add:
Cobalt Oxide 2%
Rutile 4%
For a rich, deep, mottled blue.
However, at Chris Shafale's suggestion, I tried the following:
Cobalt Carb 1%
Red Iron Oxide 2% (RIO)
Rutile 4%
and got the same texture, with a rather more muted-greenish blue. Very
attractive, just different.
Then I tried:
Cobalt Carb 1.25%
RIO 2.00%
Rutile 4.50%
and got a slightly paler blue, more green. Also nice.
I also tried, instead of the other colorants:
RIO 7% and 10%
and got, respectively, a deep, rich, translucent, very glossy brown with
some gold flecks along the rim, and the same brown with large, lighter,
reddish areas. I really liked the 10% iron test.
I want to try this with a prodigious amount of iron next (like maybe 20% or
so), and see if it turns metallic.
I then tried the base with 5% rutile only. Well, that was the plan, anyway.
I apparently didn't wash out the container very well, though, because my
rutile base ended up a very pretty, pale purplish blue. It seems more purple
under fluorescent lights (and outside) than under incandescent.
It's hard to believe such a small amount of cobalt carbonate could impart
this much color to a 500 gram test batch. Well, I'm still learning. That's
what I get for being sloppy, huh?
That little boo-boo might turn out to be a rather nice glaze, but it did
kind of mess up my subsequent tests, which were for layering, so I won't go
into those. I'll try them again later.
I found a recipe for green which looked similar to my Opal Blue base. Also,
Chris suggested that she'd read about cobalt greens prospering in
high-alumina environments. I altered the green recipe slightly (decreased
the EPK) to the following, which Chris had also suggested:
Opal Green/Blue
EPK KAOLIN.......... 30.00 27.78%
FRIT 3134........... 50.00 46.30%
SILICA.............. 20.00 18.52%
RUTILE.............. 5.00 4.63%
*Cobalt Carbonate.... 3.00 2.78%
========
108.00
CaO 0.68* 10.02%
MgO 0.00* 0.03%
K2O 0.00* 0.10%
Na2O 0.31* 5.13%
TiO2 0.24 5.00%
ZrO2 0.00 0.05%
Al2O3 0.42 11.25%
B2O3 0.63 11.46%
P2O5 0.00 0.07%
SiO2 3.58 56.65%
Fe2O3 0.01 0.24%
Cost/kg 2.41
Si:Al 8.54
SiB:Al 10.04
Expan 7.30
The first test, I ran straight, as listed above. It came out with a lovely
blue-green ground, with thicker areas similar to Opal Blue, only slightly
lighter.
The second test, I added 5% alumina. It came out uniformly, and very nicely
textured blue-green. Thick areas were quite dark.
The third test, I added another 5% alumina, for a total of 10%. It turned
out a rather unremarkable brownish black with hard-to-see blue highlights. I
liked the first one best, but my daughter liked the second one.
So, that's the story on Opal Blue and Green so far.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
Cindy Strnad on sun 18 mar 01
Oops!
Sorry, guys. I forgot to post the cone temperature with these Opal Blue
glazes. All the glazes I posted were fired as follows:
300 degrees F/hr to 2100 F
100 degrees F/hr to 2200 F
Soak 45 minutes: Cone 6 half-way bent
Cool naturally to 1800 F, hold for 1 hr.
Cool at 100 F/hr to 800 F
Cool naturally
Opal Blue doesn't require the cooling cycle, but I expected some of the
other glazes to need it.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
Les Crimp on sun 18 mar 01
Cindy -
I liked the look and sound of your Opal glazes but could not find what cone
you fired to.
Les Crimp on that Island in the Pacific.
lcrimp@home.com
Don Curtis on mon 19 mar 01
What temperature are you firing to?
Thbanks
Don
friedlover on tue 20 mar 01
Cindy, What cone?
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