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cone 10 teal gloss tests (long)

updated fri 2 apr 04


Dan Dermer on wed 31 mar 04

Dear all,
I thought I'd share some recent glaze tests with Clayart, since y=92all a=
always sooooo generous with your collective expertise.

First, some background on what I was looking for and why=85 I finally ga=
ve up
my day job in high tech. As of March 1st, I=92m a full-time potter! Yay=
(of course I have no idea yet what this means, but I=92m still giddy and
thrilled to be in my studio every day instead of a cubicle=85).
Coincidentally, on my last business trip for my old job, the nice lady
sitting next to me liked my work well enough to order a dinner set for he=
son who=92s getting married =96 my FIRST commissioned dinner set! Now th=
tricky part=85 her chosen dinner plate style is a square plate (I had nev=
made square plates =96 can you do that on the wheel?? :-), AND the glaze
selected was a copper/barium blue green (Coleman =93Teal=94) combo I use =
vases and jars.

So, I accepted the commission figuring I=92d learn how to make the square
plates (THANK YOU Lee Love for excellent instructions in the archives=85)=
, and
set out to find another glaze with color similar to Coleman Teal. I had
tested Coleman Teal and found that it leached badly in a 3-day vinegar
test =96 vinegar had a bluish tint to it, and took the metallic patina ri=
off the surface of the pot. Not something I=92d ever want on a dinner pl=

Following are the tests for a Coleman Teal substitute, and special thanks=
June Perry for offering a substitute glaze base (Perry=92s 8303) and advi=
ce on
finding a food-safe alternative; we traded a couple of emails on test
strategies. The best color match turned out to be from an entirely
different glaze =96 Susan Filley=92s =93Emerald=94 using her jewel glaze =
base. This
is GREAT since the glaze contains no barium, and doesn't even use copper =
its color.

Pictures of the original glaze, test tiles, and the closest match can be
found here: (click on =93Teal Glaze=94 album)

Read on if you=92re interested in the 6 different glazes recipes I tested=
along with comments on how they turned out. Mostly, these tests yielded
glossy blues instead of teals. I did not want to test glazes with more t=
5% barium carb, or 3.5% copper due to fears of leaching. I'm sure there =
further avenues of testing, and I welcome suggestions from the experts...=

All the best-

Original + Test Recipes

Coleman Teal
This is the color I was trying to match -- a beautiful translucent teal a=
dark-ish blue glaze, with nice copper crystals forming on surface. I use=
copper instead of the 6% specified in the Coleman=92s =93Glazes I Use=94,=
but it
still leaches in a 3-day vinegar test. The first two pictures in the Yah=
photo album show this glaze on the outside of a canister (and lid) with
other glazes layered over it. It crazes on both BMIX and Turner Porcelai=
but is quite beautiful.

Custer 47.3
Flint 15.3
EPK 7.7
Gerstley 4.5
Whiting 16.2
Barium Carb 9

Copper Carb 5.0
Cobalt Carb 0.5
Bentonite 2

June Perry=92s 8303 base
Came out a really nice transparent blue glossy that crazed on my porcelai=
June had designed this base glaze to be food-safe for a copper-bearing
glaze. It wasn=92t teal enough for a good color match, even when raising =
copper to 4%. I did not test with higher percentages of copper.

35.90 Custer
11.70 Whiting
8.80 Ferro Frit 3134
7.8 Barium, but subbed
5.0 Barium Carb
2.1 Strontium Carb
15.60 EPK
20.20 Silica

3.5 Copper Carb
0.5 Cobalt Carb

Hopper=92s Shiny Glaze base
This is from Hopper=92s =93Color Spectrum=94 glaze book; I filled out th=
e glaze
with choices of additional flux =96 strontium, boron, and barium =96 like
Coleman Teal - but less barium and copper. It came out a nice transparen=
blue glossy, with a slight hint of the teal color I was looking for, but
basically a glossy blue. I suspect that the key to the more peacock colo=
is a higher percentage of barium, and/or copper in this kind of base glaz=
Slight crazing on BMIX and Turner porcelain.

35 Custer
17 Ball Clay (OM4)
12 Whiting
19 Silica
9 Gerstley Borate
5 Barium Carb
3 Strontium Carb

3.5 Copper
0.5 Cobalt

Jewel Glaze (from Susan Filley in Ceramics Monthly Sept. 2001)

24 Whiting
28 Custer
20 EPK
28 Silica

For Emerald add:
0.4 Chrome Oxide
0.5 Cobalt Carb
5.0 Gerstley Borate
Emerald was the closest match to the original Coleman teal; it didn=92t
craze, and has a nice glossy translucent surface and feel. Admittedly, t=
color is a bit more strident teal-green than the original Coleman teal-bl=
but this looks to be a good food safe glaze=85 I plan to use it for the
dinner set!

For Sapphire add:
3.0 Zinc Oxide
0.3 Chrome Oxide
1.0 Cobalt Carb
Sapphire was not to my liking. I think the Zinc makes the color more opa=
and flat, not a very interesting blue. Might be worth testing again with=
the Zinc.

Jewel Glaze variation 1 (I replaced 5% of the whiting with 5% Barium Carb=
and used Coleman Teal colorants)
19 Whiting
5.0 Barium Carb
20 EPK
28 Silica
28 Custer

5.0 Gerstley Borate
3.5 Copper
0.5 Cobalt Carb
This glaze is yet another glossy transparent blue with tiny yellowish
crystals forming in the surface. Pretty, but not what I was shopping for.
Crazed on both BMIX and Turner porcelain.

Jewel Glaze variation 2 (I replaced 10% of the whiting with 5% Barium Ca=
and 5% Dolomite, and used Coleman Teal colorants)
14 Whiting
5.0 Dolomite
5.0 Barium Carb
20 EPK
28 Silica
28 Custer

5.0 Gerstley Borate
3.5 Copper
0.5 Cobalt Carb
This glaze identical to variation 1, a glossy transparent blue with nice
little crystals forming in the surface. Crazed on both BMIX and Turner