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Humboldt Potter

High fire black and white glaze question

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I am experimenting with creating black designs on white, Cone 10 porcelain, but so far I've not been able to get a glossy black brushed design without pitting. I need some suggestions on what techniques have worked. It's very frustrating to spend so much time creating and painting a design and then not having the finish be beautiful and smooth.

 

Here's what I'm doing: I'm using Cone 10 Glacia porcelain (anyone have any issues with this clay? It's new to me, throws well and is a beautiful white color). On greenware (or bisque, sometimes), I brush on designs using either Amaco Velvet Jet Black underglaze or Amaco LUG-1 Black (experimenting with both), then I bisque to Cone 06, long, slow 14 hour bisque, then spray with Reeve's Clear glaze (or dip) and fire in a reduction gas kiln to Cone 10-11, light reduction. The major issue is that the black sections come through the clear glazed surface and are pitted or bubbly and metallic looking, even though I spray or dip enough Reeve's Clear to cover well. The pitting seems less if the brush strokes are watered down, but that doesn't give the true black look. Is there something else I should be using to brush on my designs other than these underglazes?

 

I'm willing to try brushing over or under, to use any other kind of black formulation in order to get these high fired black and white designs. Should I be using something else to achieve the crisp, black design? Maybe brushing something over the clear, rather than under? Or mixing up something using Mason stains that won't run? Is there anyone who has had success with this?

 

I can't brush on the normal Cone 10 glazes (like Mirror Black), since they run on vertical surfaces and won't result in the crisp look I'm going for.

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neilestrick    1,379

Those underglazes are not made to go to cone 10. They are melting out and interacting with the glaze. You'd be better off making a black slip from your clay body.

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Those underglazes are not made to go to cone 10. They are melting out and interacting with the glaze. You'd be better off making a black slip from your clay body.

 

 

what would you use as the black colorant?

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neilestrick    1,379

Those underglazes are not made to go to cone 10. They are melting out and interacting with the glaze. You'd be better off making a black slip from your clay body.

 

 

what would you use as the black colorant?

 

 

You could use a black mason stain, or roughly 10% red iron oxide and 2% cobalt carb. Test it.

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