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Black Slip Turning Grey In Firing


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Morning everyone hope you all had a good, productive weekend.

 

I've just fired a glaze run and am hoping you can help.  I used mason black underglaze to colour ball clay slip. Applied to just thrown items, drying each layer before applying next. A total of three layers. I didn't glaze over the "black" half of the pot, wanting a distinct contrast to a white glaze on the rest of the pot. The result was a matt grey section.  Is this because I didn't dip in transparent glaze? Or should I have used an oxide rather than the underglaze. I throw with a stoneware that fires to a light grey.

 

Any suggestions would be greatly appreciated.  Thanks and have a great day.

 

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I would use a kaolin instead of ball clay--should have brighter colors. About 10% dry stain, 90% kaolin is a good starting point.

If you started with a liquid underglaze (~30% stain I believe), it may be possible to thin it out to about 3 times the volume.

 

A clear glaze would also help, but mostly just in the vibrancy. Sometimes I will make clear very very thin to retain more of the natural feel with just a slight gloss. The black slips I have worked with were black enough after the bisque firing.

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andrea, you did not mention the crawling of the white glaze.  do you have a way to prevent that or do you need help with it, too?

Thanks, I think it is just a too thick an application of the glaze. My pouring out has been a problem. I take too long to pour out. I've had a little problem with my left hand shaking while I pour with right hand and then taking too long to pour out. I'll switch to pouring with left hand and emptying with right.

 

Although it's a fault in my process I quite like the texture that it brought out. But saying that these items are not going to be marked for sale.

 

Which black stain did you use and what % of stain did you use?

I didn't use stain. I just added underglaze to slip. I had done some other pots the same way. I've now covered the applied slip with underglaze and bisqued them and they look much better. These were thrown with a white groged clay and I'll glaze with transparent, so hopefully I'll achieve the result I was looking for.

 

Having said that do you think I should glaze the black sections? I was trying to go for a "natural" textured black as opposed to a shiny one.

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