Ginny C's Profile
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- In the Studio (32 posts)
- 02-April 10
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- Jun 03 2013 08:39 PM
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Posted 3 Jun 2013A PRIME cause of bloating is that in the bisque firing there is not enough OXYGEN present (and able to circulate thru the wares) in the chamber to allow all of the trace materials that require oxygen to be present for the reactions to go to completion.
This can happen due to poor (or no) local pickup ventialtion, or loading a kiln tighter than usual for the same oxygen flow from the vent. Particular issues can happen with the interior pieces when one object is inside another object which is inside another object... and so on (nested bowl forms, for example).
A clay body suddenly containing slightly more carbonaceous materials than "normal" can cause this to happen in the same kiln, with the same vent system, on the same firing schedule.
Then in the glaze firing these compounds can cause out-gassing that gets tapped in the vitrifing clay.... and bingo. Bloating.
Another issue is the potential for slight levels of reduction happening in the clay body as carbonaceous materials try to burn.... but can't. The iron compounds get reduced to the Fe) state... which is a powerful low temperature acting flux on silica... and this can cause a brittle iron fluxed glass to form near the nodules of iron. These later can become overfired and start to vaporize also as they are tiny "overrfired" pockets of melt.
When we all bisque fired in fuel fired kilns (I still do) ... that could easily have large volumes of oxygen flowing.... this was less of an issue than maybe it is today with most folks bisquing in electric kilns.
So, is it helpful to leave the spy holes open, or one or two of them, during the entire bisque firing?
Posted 18 Apr 2013The kiln wash worked...or at least the dish did not warp. I'll post a photo.
I appreciate all the suggestions. I've had a problem in the past with the feet of a dish pushing up just enough to show through after firing, so I thought putting this one on something would do the same thing. Perhaps my earlier pieces were just too thin. This one is certainly thicker.
Now to see if the glaze ruins it!
(enlalrge the photo to see the pattern, from an old doily and a nylon lemon bag.)
photo 1.JPG (94.91K)
Number of downloads: 60
Posted 17 Apr 2013I've never used kiln shelf paper, but now I know what it is. 3 questions:
Do you make wads of it because using it flat would still not allow a dish to slide on it?
With wads, isn't there a chance that the bottom will sag where it is not supported?
And finally, are the wads re-useable?
After calling Amaco, I used kiln shelf wash dry under the big dish.
I bought "play sand" very cheaply at a building and garden supply store, but not knowing if it was really silica sand and seeing that it was wet, I decided to try the kiln wash first. I'll report tomorrow how well it worked.
Posted 7 Apr 2013Thanks for the kind words, Wyndham, but parts of the bowl are really rough...it is not acceptable as it is. I think it looks better in the photo than it is! My major question, though, is how to make the glaze useable again. It's not like the yoghurt consistency that some brushing glazes are. This one now cannot possibly be brushed on...it is too stiff.
Posted 5 Mar 2013Ah! Well, mine is much taller so it doesn't look like a yo-yo, but I see that his does.
Thanks, Patti, for your link...another way to do it!
I wonder if anyone noticed that I said I'd chattered the pot, which means that it was already leather hard and then some! I didn't think about that until I started to push in to form the flange. Of course it was way to stiff to work right, and I ended up having to pretty much hand carve the thing! At least it didn't completely ruin the chattering, but it is an experiment I won't repeat on a leather hard pot!
- Member Title:
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- 74 years old
- May 26, 1939
- Fort Wayne, IN
- functional, beautiful pots. experimenting, combining glazes
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