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Advice on a Raku glaze


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#1 Kohaku

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    Huffing cobalt over a Raku kiln

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Posted 01 May 2013 - 02:25 PM

I've been using a glaze called 'Egyptian blue' that I pulled off the web. Here's the chemistry.

Egyptian Blue
Soda Ash 30.5
Lithium Carbonate 8.5
EPK 22.5
Flint 38.5
Black Copper Oxide (added) 2.5
Bentonite 1.0

There have been a couple instances where this glaze yielded a lovely mix of vibrant blue-greens, with every shade of red and orange on the sides. Here's an example.

Posted Image


More often, though, I get either an algal green, or a brick red (or copper). For an example of the former, see below.

Posted Image

I'd like to get the first result more consistently. Yes- I know Raku is a chaotic process...

My theory is that the first result stemmed from several factors...

1) Less maturity at the tail end of the firing process (and thus a 'sandstone-like' texture)
2) Thick glaze application
3) Fast transfer of the piece to the reduction chamber
4) Intense but brief reduction, with the piece pulled early and rapidly cooled

These were the conditions for the firing for the piece at the head of the page. However, when I tried to duplicate these conditions recently, here's what I got...

Posted Image

Not bad... but not exactly what I'm going for.

Any suggestions appreciated!
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#2 neilestrick

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    Neil Estrick

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Posted 01 May 2013 - 02:50 PM

As you said, Raku results will vary based on firing temp, glaze thickness, degree of reduction, cooling speed, etc. You need to experiment with many pots, only changing one variable at a time to see what gives you the best results. It different for every kiln, every firing situation.
Neil Estrick
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#3 Kohaku

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Posted 01 May 2013 - 03:34 PM

As you said, Raku results will vary based on firing temp, glaze thickness, degree of reduction, cooling speed, etc. You need to experiment with many pots, only changing one variable at a time to see what gives you the best results. It different for every kiln, every firing situation.


Totally agree.

Mostly, I was curious as to whether anyone had used a glaze with similar chemistry/characteristics, and had suggestions on ways to narrow in. There are a lot of variables to tweak otherwise!
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#4 Marcia Selsor

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Posted 02 May 2013 - 06:06 AM

The brick red piece is hotter than most of the others. The last piece was cooler, you can tell by the bubbles not smoothing out. The first three pieces look like the glaze is too thin and uneven.
So, you just have to be consistent in how you apply the glaze and when you pull them out and how fast you get them into the reduction.

Marcia




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