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glaze test for cream breaking red, cone 6, ox., 5 versions

updated mon 11 feb 02


Alisa og Claus Clausen on sun 10 feb 02

Glaze test for: Cream Breaking Red, cone 6, ox.
4 Versions

Source: Clayart Archives
Credited to:

All tests fired on white, iron flecked, mid-range stoneware.
Fired to cone 6 (1220c) in oxidation.

Firing ramp:
100c (212f) per hour to 600c (1112f)
150c (302f) per hour to 1100c (2012f)
100c per hour to 1220c (2228f)
15 - 30 minute soak depending on matts and glosses used.
cool down 100c per hour to 900c.
Natural cool down to 150c (approximately 15 hours)

In these tests I substituted the Local Frit #623 for G.B. Strontium Carb.
for Barium in 4 different combinations.

Original recipe:
35 Gerstely Borate
15 Kona F-4 Feldspar
10 Whiting
5 Barium Carb.
10 Flint
13 Tin oxide
2 RIO gives 90 grams

All raw materials measured up or down to nearest whole decimal.
Oxides used on percent basis to a 100 gram batch of glaze.

In all trials, Kona F-4 is subbed with Forshammer Spar.

Test No. 1, above recipe

Resulted in:
a creamy white semi gloss glaze with small, very tight crystals
throughout. It breaks red, just like the name. It is a pinkish red, and
in some areas a very pale rust red. Smooth surface and stayed where glazed.

Test No 2.
Gerstely Borate plus Strontium subbed for Barium
Resulted in:
Very similar to above in surface, but overall background color is slightly
more yellowish than whitish cream.

Test No. 3.
Local Frit #623 subbed for Gerstely Borate plus Barium
Resulted in:
Very very similar to test no. 1, except it ran where very thick at one edge
of test tile. Small tight crystal formation very attractive. Has an
surface like curdled milk, but very smooth. More ground between the tiny
crystals, giving a slightly grayer tone to overall glaze color. Test no. 1
had more red breaking than this tile.

Test No. 4
Strontium carb. subbed for Barium Carbonate
Local Frit subbed for Gerstely Borate
Resulted in:
a well covering cream white semi gloss glaze, with small tight crystals
throughout. No red breaking on this tile and a single drip where very
thick on one edge of tile. Similar to above test.

Test no. 1, original recipe, was the reddest. However, tests no. 3 and 4
have a very attractive overall surface with tiny and slightly distinct
crystals. All had very smooth surfaces. I will work further with the last
two tests to see if they break redder on larger test pieces.

Regards from Alisa in Denmark