Slip smudging at glaze firing

[Trazar]

Hi there I have had an issue of slips smudging at the glaze firing. Using a white stone ware clay (1200 - 1290) and slip (bought as mixed and ready to apply) the bisque firing was as expected. But after the glaze firing at 1230 a few of the pieces the slip pattern has smudged and the the image lines are blurred. See photo attached. The only thing I can think that I may have done wrong at greenware stage is to apply the slips on to a too dry surface? Has anyone had this experience before? Thanks Trazar

 

 

[Chris Campbell]

This is called "bleeding" and it is an interaction between the colorant and the glaze. Some people love the effect and actually go for that exact look.

 

Using underglazes instead of slips reduces this ... you can also try firing the slip or underglaze to Cone 018 ... just enough to set it ... before the glaze is applied and fired. But some colors are just prone to it because they flux at high temps and move.

 

All clear glazes are not alike and some recipes cause more bleeding and color changes than others so try another kind and see if it does better.

[Marcia Selsor]

That is a "flowing blue" antique look.

Chris makes good suggestions. I don't think it is smudging as much as fluxing. You could try using mason stains in a slip base rather than commercial products.

If cobalt was used in the slip, it could be blushing or fluxing.

 

Marcia

[Lucille Oka]

Harden on your underglazes; apply your underglaze decoration to dry greenware, when dry, place the ware in your regular bisque load.

 

If you sand your greenware prior to underglazing, application may be difficult. Run a damp sponge across the surface of the greenware before you apply the underglaze.

[Trazar]

This is called "bleeding" and it is an interaction between the colorant and the glaze. Some people love the effect and actually go for that exact look.

 

Using underglazes instead of slips reduces this ... you can also try firing the slip or underglaze to Cone 018 ... just enough to set it ... before the glaze is applied and fired. But some colors are just prone to it because they flux at high temps and move.

 

All clear glazes are not alike and some recipes cause more bleeding and color changes than others so try another kind and see if it does better.

 

 

Hi Chris

 

Thank you for your reply.

 

I'm a real novice as I understand most underglazes are quite low firing 1030 to 1060? I've found that firing to this temperature for domestic ware the item gets chipped very easily?

 

Bit confused about firing slip just enough to set it? I applied the slip to quite dry greenware and bisque fired it, then I glaze fired it. Shouldn't the slip have set at the bisque firing? The other confusing thing is that I have used this glaze with this slip before and haven't got bleeding?

 

Trazar

[Chris Campbell]

Some Underglazes like black, dark blue, dark green can be fired as high as Cone 10 and only get darker .... Others like pinks, reds, violets burn off so you would have to do test pieces to see what happens to your color of choice. I believe the Amaco catalog ( and maybe even their website ) has images of the results at various temps.

 

That is what I meant ... Fire the raw product before glazing.

 

Weird that it worked before but suggests that something changed. Did you fire it hotter? Or use a new mixture of either slip or glaze? Sometimes formulations of commercial ingredients change without notice. If all you want is the design in black or dark blue then underglazes might be the answer.

[Trazar]

Some Underglazes like black, dark blue, dark green can be fired as high as Cone 10 and only get darker .... Others like pinks, reds, violets burn off so you would have to do test pieces to see what happens to your color of choice. I believe the Amaco catalog ( and maybe even their website ) has images of the results at various temps.

 

That is what I meant ... Fire the raw product before glazing.

 

Weird that it worked before but suggests that something changed. Did you fire it hotter? Or use a new mixture of either slip or glaze? Sometimes formulations of commercial ingredients change without notice. If all you want is the design in black or dark blue then underglazes might be the answer.

 

 

 

Thanks You Chris