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^6 cream breaking red glaze test results

updated sat 31 may 97


John Post on wed 21 may 97

Collen Raynor recently posted Tom Buck's Cream Breaking Red glaze. She
tested it and found that it is "a predominately rust glaze with a cream
colored speckel". This is the recipe she posted...

Glaze name: Tom Buck's Cream Breaking Red
Cone: 6-7
Firing: Oxidation

41.00 G200 feldspar or equal
22.00 Gerstley borate
9.00 Whiting
3.00 Strontium carbonate
25.00 Flint
100 Total

Also add:
13.00 Tin oxide
6.00 Red iron oxide

This glaze sounded interesting to me and I decided to test it on my white
stoneware body. I found that it is rust colored where thin or where it
breaks over an edge. It is cream colored where it is applied more thickly.
Even though it is not red as the name implies, I think it is quite a nice
looking cream and rust gloss glaze.

I found that the glaze tended to settle at the bottom of bucket. In order
to improve the working characteristics of the slurry I recalculated the
glaze formula to include some clay. In this new version which I call CBR-3
there is 8.4% EPK. I also replaced the gerstley borate with Frit 3134.
Wollastonite replaces the whiting and some flint. The reasoning behind
some of these ingredient substitutions is based on information I found in
the article "Getting a Cone 6 Oxidation Glaze Right For You". (This
article is located on the IMC webite. Thanks Tony!).

After I fired CBR-3 on a white stoneware body at cone 6 & 7 I found that it
has the same visual characteristics as Tom Buck's Cream Breaking Red. It
is speckly rust where thin and more cream colored where thick. A very warm
attractive glaze. The slurry of CBR-3 seems improved because it stays in
suspension better.

I tried using less tin oxide in order to cut the cost of the glaze, but the
glaze was not opaque enough with 3% or 6% tin. At 9% the glaze was opaque,
but didn't have the creamy brightness of the glaze with 13% tin oxide. I
also tried 15% superpax instead of the tin, but that glaze test turned the
rust color a dull brown and the left the creamy areas looking dingy. I'm
going to stick to using the 13% tin because it gave the best results.

The nicest looking results occured when I sprayed CBR-3 on the top 1/3 of
some pots and Bob Kavanaugh's Berry Rust glaze on the bottom 2/3. I then
lightly sprayed some Berryrust over the CBR-3 at the top. The pots came
out of the kiln with a rich cream and speckled rust color at the the top
and a wonderful deep rusty red on the bottom. The combination is
wonderful. If you don't already have it, Bob's Berryrust glaze is listed
below. It is a wonderful rich oxidation red.

Glaze name: CBR-3 (John Post's Revision of Tom Buck's Cream Breaking Red)
Cone: 6-7
Firing: Oxidation

30.6 Frit 3134
26.6 Custer feldspar
10.6 Wollastonite
2.3 Talc
3.3 Strontium carbonate
8.4 EPK
18.2 Flint
100 Total

Also add:
6.0 Red iron oxide
13.0 Tin oxide

A speckly rust glaze where thin, turning into a creamy beige glaze if it is
applied more thickly. Great in combination with berryrust. Works at cone
6 & 7. The one time I tried it in reduction at cone 7 it turned an
unattractive speckled grey.

Glaze name: Berryrust
Cone: 7-10
Firing: Oxidation

27.28 Flint
18.18 EPK
18.18 Nepheline syenite
9.09 Dolomite
9.09 Gerstley borate
9.09 Talc
9.09 Bone ash
100 Total

Also add:
9.09 Red iron oxide

Works best if applied thin. It turns greenish where it is thick. Seems to
actually yield redder fired results as the glaze ages in the bucket.

Thanks Colleen, Tony and Bob.

John Post