Extra Burned Glaze?

[ArtbyMarioOlmos]

Not sure how this happened.

I am a ceramic student at a Community College, so the kiln is collective and I didn't loaded.

I was using the glaze Mirror Black over a piece that was already bizqued with black engobe, and this is the result.

I did ask my teacher, but not a clear answer.

Any idea?

Thanks!

[neilestrick]

It could be incompatibility with the black engobe. Could be the glaze is too thick. Could be the kiln was too hot/cold. Did any other pieces have problems? Have you used the glaze with the engobe before?

[High Bridge Pottery]

I think the black on black may have oversaturate the glaze with colouring oxides and given you that burnt toast look.

[Benzine]

The only time, I've seen something like that, is when I did a Raku firing and the wares didn't get hot enough.  The glaze was boiling, but didn't have a chance to smooth out, before we pulled them out.

 

I can't say for sure, that's what the problem was, but that's what it reminds me of.

[glazenerd]

Looks like molten glaze soup to me. I ran extensive flux tests a few years back: and will venture a semi- think I know guess. Potassium and sodium fluxes become gases at high temperatures, unlike lithium and calcium that are liquid. At cone 6 they boil, like what I see above. At cone 8, there is less of a boiling look: but a series of heavy pin holing. At cone 10, pin holing that most of us have seen. Without additional info, I can only venture a guess. Potassium causes more problems at cone 6 and sodium causes more problems at cone 10: from my experiments with them. Regardless, the boiled look is highly molten fluxes boiling and off gassing. IMO Not sure an extended hold would solve this problem: suspect the sodium/potassium batch % are well over 5.00% and probably closer to 6% ( or more).

Nerd

By the way: commercial clay or mixed in house?

[Magnolia Mud Researdh]

It looks like a cone 10 shino glaze over a cone 10 temoku   glaze fired in reduction.

 

LT