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Glaze components: Line blend Tests

After having each of us having done so base material test for glazes, which were fired in oxidation and reduction for comparison, Dave now asked us to do a line blend test combining two base materials. I decided to two test one involving more tradition materials and the other using Bicarbonate of Soda, which was such a pleasant in the previous test.

1st Test: Red Clay (No.4) + Nepheline Syenite (No.13)

The quantities of each ingredient is mixed with water to following proportions:

Red Clay:

100% 80% 60% 50% 40% 20% 0%

Nepheline Syenite:

0% 20% 40% 50% 60% 80% 100%

Which resulted in this once fired to about 1260°c in oxidation (top) and 1270° in reduction (bottom):

The red clay is very strong and acts very much like a coloured slip. However, the more Nepheline Syenite is added to less opaque it becomes but also becomes much more glassy. This illustrates very nicely how a primary flux in form of Nepheline Syenite reacts with a clay, which acts as a stabiliser. If I'd go further in extending my research with these two components I may add another flux for a triaxial test.

This is a close up showing the difference of 100% Nepheline Syenite fired in reduction (left) and oxidation (right). Nepheline Syenite is the main ingredient in Shino glazes, which tend to get fired in reduction.

2nd Test: Ball Clay (No.3) + Bicarbonate of Soda (No.53)

Quite a nice way to see how the proportions of the two components change across the line blend test. Even though each cup makes up 100g of material the volumes vary.

The quantities of each ingredient is mixed with water to following proportions:

Ball Clay:

100% 80% 60% 50% 40% 20% 0%

Bicarbonate of Soda:

0% 20% 40% 50% 60% 80% 100%

My previous materials test has taught me that Bicarb. of Soda fluxes heavily so I applied less this time in order to prevent it from melting onto the kiln shelf during firing.

Here is a close up of the 100% Bicarb. of Soda in reduction and oxidation. The colours are not as green as in my first material test done a few weeks ago.

Nevertheless, I really think there may be some potential here, especially for reduction fired pottery. If I find the time I may try a triaxial blend adding a primary flux to balance the mixture. Dave suggested one of the disadvantages of using Bicarb. of Soda is that it is soluble. Thus, it will penetrate into the clay body and may cause unwanted distortions to the clay body during firing. Still worth a try I believe.

I think we all are slowly, very slowly starting understand the very basics of glazes and what endless potential there is out there, should one decide to really go down that road.


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