Refiring Bisque To Avoid Pinholing / Pitting

[tomhumf]

I've just unloaded a glaze kiln and have quite a few pinholes. They are worst on pieces I have done two layers of glaze on. Some things are fine but some with just one glaze on have pinholes. It's the same clay and bisque firing.

 

The clay is a heavily speckled stoneware, and I'm thinking I haven't been bisquing high enough. My kiln sitter kiln fires one cone lower than the cone you put in the sitter. I've been using ^07 bar thinking I'm doing a ^06 firing, but of course it's actually ^08 ! Duh

 

So reading other threads I think I'll get some ^02 bars to fire to ^03 and get some witness cones to check.

 

My main problem is I have a set of pots that I bisqued to ^08 that I really need to turn out nice. Would it be ok / make a difference to refire them when I get the new cones?

 

Thanks!

[Marcia Selsor]

You can take some very dry glaze and mash it into the pin holes with a finger nail. and re-fire.

It should be fine if you have the time. Bisque the rest of that clay hotter.

 

 

 

Marcia

[neilestrick]

Yes, you can re-bisque them. Speckled brown clays definitely benefit from a higher bisque. I'd go 04. At 03 you may find that it's tighter than you want for glazing.

[tomhumf]

Ok Marcia I will try that trick with some of the worst offenders. I've taken your advice and ordered some 03 cones to fire to 04 Neil.

 

It's occurred to me that the worst offenders were saucers and bowls I'd stacked with sand between them during the bisque. Maybe this contributed to the problem, and I might just bisque everything separately in future.

 

Thanks both for your suggestions.

[neilestrick]

Stacking is fine as long as you're firing slowly enough for the heat to penetrate.

[Marcia Selsor]

If you go hotter, the stacking as Neil says will take care of the out gaming if you fire slower.It is always good to have a full load like stacking pieces.

Marcia

[Tim82]

You mentioned that you stacked with sand between, I know from my own expiernece that any dust or foreign particles can trapped between the body and glaze can cause pinholing. In you need to fire with sand between the work once fired wash the work with water and scrub to remove an particles I found doing this pretty much 99.9% stopped pin holding with my work.

 

Things I usually start with

1 fire at a high bisque

2 ensure the surface is completely free of dust and debris and also the glaze is clean and smooth (no lumps)

3 fire the glaze to its optimum temp . Ie if it states 1080 to 1100 go to 1100.

4 soake at high end 20 mins

5 can even fire down to ensure the glaze is healing over the holes

 

If after this there are pin holes perhaps the glaze doesn't suit the clay body. You can always apply glaze over the pinholes and refire and soak. This usually covers the pinholes, but at the righ angle you may see where they were. But to a non ceramisit it would be seen.

 

Chers

 

Also if making your own glaze ensure it's blended well