Alisa og Claus Clausen on tue 20 mar 01
Dear Ivor and Clayart,
A while ago, you noticed that I had some green lines produced by my =
oxide mixture of Cobalt, Ball Clay and Rutile on a Dolomite base glaze. =
We slightly discussed the ability to fine tune what gives the Cobalt =
green. I had never seen cobalt green until I started using the Dolomite =
base glaze.
I am looking at my last WoDo White tests with colorants. There is a =
common denominator for the greens that came about with cobalt. Rutile =
in the oxide mixes with cobalt, on a Dolomite base glaze.
I would like to look further in to this for research sake, but my Hamer =
and Hamer is in the shop. What do you think? Is it the Rutile and =
Dolomite that are catalysts for the cobalt green?
Best regards,
Alisa
Hank Murrow on tue 20 mar 01
Alisa wrote in part;
Is it the Rutile and Dolomite that are catalysts for the cobalt green?
Dear Alisa et al;
My experience and that of my wife Bev (who researched this color in college
in the 60s) is that Magnesia is neither required nor need be excluded to
form this color. What IS required is Titania (whether from Rutile or
Titanium dioxide, or some other source) to turn the normally blue color of
cobalt to green. Calcium does seem to be common to all of them, however. I
use several recipes for this color, including my variation on Reitz Green,
and the recipes are all over the map. If you would like to test for this
color, try making up small cups of cobalt/4 rutile & cobalt/4titanium wash
mixtures to stripe on all your glazes. You will find an amazing # of greens
from this exercise. Meanwhile, try the original "Bev's Smile" recipe, often
simplified to just "Smile", greener over irony bodies, soft blue/green over
porcelain at C/9-10 OX or RED is given below.
BEV'S SMILE! C/9-10 Red. or Ox.
Buckingham Feldspar 42.00 (sub Kingman or Custer or G-200)
Whiting 20.00
EPK 25.00
Silica 10.00
Rutile 3.00 (try more Rutile or TiO2)
Cobalt Carbonate 1.5
Unity Formula for Smile!:
0.194 K2O 0.607 Al2O3 2.974 SiO2
0.066 Na2O 0.004 Fe2O3 0.139 TiO2
0.737 CaO 0.001 P2O5 4.9:1 Si:Al Ratio
0.004 MgO
Cheers! Hank in Eugene
Jocelyn McAuley on tue 20 mar 01
Hello Hank, Alisa and Ivor,
I just wanted to chime in with my occurance of cobalt green. I've
noticed this green separate out in my highfire macro-crystalline tests.
The base glaze (Frit 3110, zinc oxide, silica, titanium dioxide) with
cobalt added yields blue with blue crysals, however the addition of 10%
dolomite yields blue crystals with very distinct green halos (on a
purple background). I've enjoyed this very distinct green highlight. I
find it interesting that it doesn't seem to come through in the background
color, or in the main crystal body.
Thanks for reminding me of this! I'll have to play with it more in my
next batch of tests.
Jocelyn
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, OR
Ron on wed 21 mar 01
I too have gotten a cobalt green in Cone 10 oxidation firing. I use a blue
cobalt slip on some of my pots. I use a base glaze that contains Dolomite
and under this glaze the blue slip will turn green. I was wondering what
caused this but reading your post about using Dolomite and getting the same
result....it must be the dolomite.
Ron
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Jocelyn McAuley
Sent: Tuesday, March 20, 2001 12:21 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Cobalt green/Ivor
Hello Hank, Alisa and Ivor,
I just wanted to chime in with my occurance of cobalt green. I've
noticed this green separate out in my highfire macro-crystalline tests.
The base glaze (Frit 3110, zinc oxide, silica, titanium dioxide) with
cobalt added yields blue with blue crysals, however the addition of 10%
dolomite yields blue crystals with very distinct green halos (on a
purple background). I've enjoyed this very distinct green highlight. I
find it interesting that it doesn't seem to come through in the background
color, or in the main crystal body.
Thanks for reminding me of this! I'll have to play with it more in my
next batch of tests.
Jocelyn
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, OR
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