Posted 13 August 2013 - 03:16 PM
I think someone under that subject mentioned it might be something called mildew and that it came from under fired bisque or something. Or maybe it was moisture in the piece that caused the mildew that only appeared once fired. Like I said I tried to find the subject again but couldn't. Maybe someone here that has gotten the search engine to like them can do a search and find it?
Sorry that probably no help at all.
Posted 13 August 2013 - 03:18 PM
This is a light buff body, I can't imagine what it could be.
I don't think iron,,,,any thoughts?
Is the newsprint the pots were wrapped in old enough for the ink to contain lead? I believe that newsprint became lead-free at some point in the 70's...? But prior to that, there was plenty of it in dark newsprint. Certainly enough to cause an effect on pots, I suspect. Interesting.
Posted 13 August 2013 - 04:57 PM
That is interesting about the lead. It was 1992. LOL.... I wonder? I'm going to try scrubbing them before I re-bisque any more. I don't think mildew cause it wasn't there before I re-fired, yesterday. I'm gonna glaze test on a small pot in a test kiln and cross my fingers. I'll have to but a little kiln god on it and do a little dance. The dance is optional.....
Posted 13 August 2013 - 06:56 PM
I had some pots that students left and so I used them for glaze testing. Some of them had spots like that after bisque firing. That caused problems as the glaze did not fire well. I finally decided the clay had grown a crop of organics while sitting wrapped in newspaper. A higher bisque cone took care of my problem. Your problem will let you know if you guess wrong.
Posted 13 August 2013 - 07:06 PM
Hi Shirley, Do you remember how high you had to bisque? I think these were originally fired to 07.
Posted 13 August 2013 - 07:27 PM
Posted 14 August 2013 - 08:27 AM
I've very recently unpacked a wet bin load of old bisque in old newspapers that has sat in a celler for 9 years. The pots had the most outstanding green, black or white moulds growing on them!!!
All went into 2 big bisque firings at Cone 06 and all but one look great again, several are in a glaze fire now. The odd one looks a bit discoloured but that is probably with a smear of slip. I was experimenting with slip for a while and figure I packed this one without a good clean first....but... I have an opaque satin black I want to test so this little pot will be it!
My vote is bisque again to Cone 06.
Art, Craft, Design, Education
Posted 14 August 2013 - 03:18 PM
I usually bisque to cone 04, so that's probably what I did with those old pots.
Posted 14 August 2013 - 10:02 PM
It is just mold, if it were mine and I wanted to be sure I got the best possible results, I would re bisque and then blow off the residue. I have done that before with pieces that have sat for 30 years, it is amazing the amount of organic and other buildup that happens over time. Last year I fired a large electric kiln that had sat for 15 to 20 years, it smoked quite a bit from all the organic material that had grown in the kiln.
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