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Aleksey

Transparent Glaze For Red Clay?

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Hi All,

 

 

IMAG0450.jpg

 

I experimented with local clay taken from the walls of the spring at Little Bay..

 

You can see the results on the photo.

 

On the right is filtered clay, one firing to 1000 C.

It is cracked a little, it is my fault, it happened before firing.

 

In the middle there is a small ball, filtered clay, one firing to 1260 C

It is very hard, very smooth and I can easily cut the glass by any side of it.

 

To the left is non-filtered clay, 1000 and 1260 C ( some doubts as color did not changed a lot )

Before second firing it was covered by dip-in glaze, I was told that it is clear

potash, feldspar, whiting,kaolin, silica.

 

I want to find a way to glaze this clay that will preserve it's color as much as possible.

Now I know only that salt glazing can help.

 

Do you have any ideas?

 

 

SmartsyArtsy likes this

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The richer coloured feet look shiny, did you glaze these also? Do tests with a variety of clear glazes. firng and cooling schedules can affect the opacity of some glazes as can the thickness of glaze application.

Seems great clay w ithstanding 1260 C as at a bisque it looks quite rich in  iron.

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> The richer coloured feet look shiny, did you glaze these also?

 

You are right, I looked again at it, feets look glossy near the edge of the glaze. Glaze was water based, perhaps it soaked into the clay.

So some soluble ingredient of the glaze worked right way. What it could be: potash, feldspar, whiting,kaolin or silica?

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What do you mean it was water based? I thought all glazes were suspended in water.

 

If you fire clay hot enough then it will turn into a glaze, that is what I thought was happening but the small ball confuses me as that was fired as hot but looks nothing like the feet.

 

Could be something to do with the filtering process removing some flux from the clay.

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So the small ball and the vessel on the left are of the same clay body?? Fired to the same temp??

Nto sure which colour you are trying to preserve, in its raw state? I find that higher temp firing will alter the colour of the clay to a greater extent depending on the clay body.

The water would have soaked into the clay but unless there are solubles in the glaze, or the clay is of an open nature, the glaze ingredients, unless soluble do not penetrate into the walls on glazing. to my knowledge, there are no solubles in the above ingredients..

Suggest you do test tiles

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> Babs, on 10 Sept 2014 - 09:43 AM, said

> So the small ball and the vessel on the left are of the same clay body?? Fired to the same temp??

 

Yes, the clay is the same and I was told that the temperature is the same, because they always fire to 1260 for glazing

But I cannot be sure as it was done without me. Perhaps temperature was lower in this case.

 

> Nto sure which colour you are trying to preserve, in its raw state?

 

I more like color to the right, I don't want to fire to 1260 again.

 

> Suggest you do test tiles

 

Yes, but which glazes to test?

 

Will salt glazing help?

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In my experience, all stoneware clays other than white will be darker after the glaze firing than they were after bisque. Buff and lighter brown clays are pink after bisque, then turn their final shade of brown in the glaze firing. Dark browns are milk chocolate after bisque and nearly black after glaze. Red clays are as in your pictures.

 

Low-fire terra cotta clays remain lighter red because they are never fired hotter than bisque. But earthenware does not have the strength of stoneware. You can apply a low-fire clear glaze to your cup and fire it in your next 1000C kiln load. It will need to have its own little place on the shelf with nothing touching it, as in any glaze firing, but the rest of the kiln load being a bisque firing doesn't matter. All that matters is the temperature. Your pieces will not vitrify to maturity at 1000C and so will not be as strong as they would be if fired to 1260C. You have a choice - color or strength, you can't have both.

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no matter what glaze you put on the clay, you're going to lose the color you like once the glaze fires into it.  pretty much same concept with wood + finish/varnish/urethane/oil etc where you get more saturation even with a true "clear" coat applied to the surface.  salt glaze will have the same outcome, darker "fluxed" finish.

 

only way i can think of preserving the low-fire color is by making a slip or glaze that ends up that color when fired to the higher temp.  that right there will take a good amt of testing.

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