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TJR

About Raw Glazing

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Seems to be a lot of discussion on the blog about raw glazing-meaning glazing your pieces without bisquing. I thought I would help out here by describing how it's done

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There are two methods of raw glazing. [A cautionary note;I may be making some generalizations here, but I am speaking from experience. As always, test,test,test.]

Method1;In this method, pots are glazed on the inside when they are leather hard. Then you wait until the piece is bone try and glaze the outside. The advantage is that you do not have to adjust your glazes, and can use what you are currently glazing with.The disadvantage, is that when you glaze a bone dry piece on the outside, there is a physical shock, as the piece is moving from bone dry back to wet in a short amount of time. I used this method at a production pottery I was working at in Scotland. About 50% of our work was not glazed on the outside, as we were wood firing and the fly ash glazed the piece. Potters such as Mark Hewitt, Svend Bayer, and Robert Barron use this method. They fire very large kilns, and have a long pre-heat. They also salt certain parts of the kiln, so do not require a lot of glaze on the outside. They do also use glazes on the outsides of some pieces.

 

Method 2. Leather hard glazing. In this method, you are glazing the entire piece by dipping into a bucket of glaze the way you would glaze a bisque pot. Obviously, you would not be using glaze tongs.The beauty of this method, is that there is no physical shock to the pots as they are already leather hard. The difficulty comes in glazing large bowls and plates.The clay should be fairly open. Porcelain is a little more difficult. You will sustain losses with both methods. In the leather hard method, you have a continuous flow, as you must glaze slightly after leather hard.

Here are some raw glazes for method 2. Note that the glazes have 25-35% plastic clay in the glaze. You can directly substitute ball clay for kaolin, and you could add bentonite.[not too much-3%-5%].

These glazes are all cone 9 cone 10.

Chun

Ash 33

Pot spar 33

Ball 30

Red Art 4

----

100

 

Killer Ash [bray]

Wollastonite 25

Neph Sy 25

Ball 25

Wood Ash 25

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100

Bentonite 3%

 

Tom Roberts White [mine]

Spar 35

Ball 30

Whiting 20

Flint 15

--------------

100

 

I prefer the leather hard method of raw glazing. This is a method that I used at a pottery in England where I also worked. I currently do not raw glaze as I transport all of my pots to another location for stoneware firing. I also throw porcelain which is a bit tricky to raw glaze.Shiny glazes are a bit tough to attain, as they have less clay in them.

Remember, before you make that 10,000 gram batch of glaze, test, test, test.

Tom Roberts.[TJR].

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Why, if you only raw glaze the inside you do not need high clay content glazes, but if you do the whole thing you do?

 

 

It has to do with the clay body shrinking. If you let the pot become bone dry on the outside, then you can glaze with your regular glazes. If you glaze the pot inside and out at the leather hard stage, the pot shrinks as it dries. The inside would be O.K., but the outside glaze would not shrink, and would just be loose on the pot. I hope I am explaining this all right.

TJR.

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Why, if you only raw glaze the inside you do not need high clay content glazes, but if you do the whole thing you do?

 

 

It has to do with the clay body shrinking. If you let the pot become bone dry on the outside, then you can glaze with your regular glazes. If you glaze the pot inside and out at the leather hard stage, the pot shrinks as it dries. The inside would be O.K., but the outside glaze would not shrink, and would just be loose on the pot. I hope I am explaining this all right.

TJR.

 

 

That makes sense. Thanks.

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