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cobalt green at ^6 / reitz green recipe

updated sat 1 jun 02


Malone & Dean McRaine on fri 31 may 02

Aloha from Kauai everyone: What a hot topic! I'm very interested in Cobalt
Greens because I have been using Reitz green for years and at its best, it
is beautiful (to me and lots of customers,anyway).This is the recipe I use.

Reitz Green

Neph Sy 70
Petalite 15
Ball clay 8
Whiting 5
Gerstley Borate 2
Cobalt Carb 1
Rutile 2
Bentonite 2

Deflocculation may be necessary depending on your water, I think, let it
stand for a day and if it still is pudding-like add:
Sodium silicate 3 tbs/ 5 gal bucket (20,000g)
soda ash 0.3

Thicker is a matt lighter green, thinner is a semi-matt darker green,
thinner still is satin gray-blue. I like it best when the dark & light
green are both present.It tends to break white around edges on white
clay. I use Dave's porcelain from Laguna. I've also had some nice but
inconsistent results with it on red stoneware. I single fire but I don't
think that matters. I fire ^10 oxidation but I think reduction is OK too.
Temperature matters, it burns out at ^10 and I always fire it in the
coolest part of my kiln to ^9 touching. I had to run quick test on a new
batch once and stuck some tests in a ^6 firing a friend was doing and they
looked as good or better than usual at ^9 so I would definitely try the
above recipe at ^6. The biggest problem I've had with it is crawling. The
high alumina content creates a high surface tension in the melted glaze and
so it is very prone to irritating little crawly flaws. Hamer suggests that
mixing fluxes will help this problem and I've modified the above by
substituting 5% custar spar for 5% of the Neph Sy. So far that seems to be
successful but I'm not sure yet. Although the glaze seems low in silica I
have a bowl that I've used a lot for years that shows no wear, stains,
discoloration or markings at all. This isn't a definitive test, for sure
but certainly is encouraging for durability.