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pottery in glass kiln

Posted: Wed Nov 12, 2014 6:43 pm
by Corlette M
Can anyone recommend a book or other source of information that would expain in detail the firing process for pottery in a glass kiln. I am looking only for general how to information- not theory. My son is taking his second pottery class and wanted to make a few pieces at home. I have finally deciphered the language of "cone firing" as it relates to temperature but still have no idea about protecting the shelves, ramp up and down speeds etc - or whether those things matter with pottery as they do with glass. And will firing glazes without an exhaust system damage the kiln ( i could still vent the kiln)? Can the same kiln wash for glass be used to protect a shelf from glaze? We have looked in several pottery books and have a rough idea of the process but I would like to be sure before risking my kilns. I am surprised that the classes didn't teach more about the firing process, but the work is all fired for the students after hours.

Or can anyone contradict what I am thinking of trying:
A piece of low fired clay will be shaped, dried and placed directly on a kiln shelf - no shelf wash or paper.
Fire straight and quickly to the temperature that corresponds to the cone (06 is 1830 degrees F)
Shut off

Glaze piece with a low fire glaze. Let dry.
put down shelf wash and kiln paper.
Fire to corresponding temp, with kiln vented
Cool down slowly? Anneal?

Sorry this is kind of all over the place and not really glass related but maybe someone is fluent in pottery as well as glass:-)

Re: pottery in glass kiln

Posted: Wed Nov 12, 2014 11:19 pm
by charlie
1st, will your kiln get to 1830? second, you'll need to know the correct temp for the glaze. cones don't correspond to a known temp, they are time AND temp. you should fire a cone that you're going to use, get to top temp, and see when it bends. some glazes need a certain amount of top temp in order to produce the required colors or effects. we can't answer because we don't know what you're going to use.

second, ceramic kilns don't anneal ware. they just shut off and cool naturally.

ceramic wash is different than glass wash; it has to last at a higher may or may not protect your shelves. i would use the back of your shelf in case the glaze runs (again, depending upon the glaze, some will, some won't).

some glazes require venting, others don't. it won't damage the kiln but it might do damage to the elements, depending upon the glaze.

Re: pottery in glass kiln

Posted: Thu Nov 13, 2014 4:34 am
by Peter Angel
Firing to high temperatures will shorten the lifespan of your elements.


Re: pottery in glass kiln

Posted: Thu Nov 13, 2014 11:45 am
by Judd
What kind of kiln do you have? If it's a glass kiln, it won't get hot enough for the pottery glaze to mature. The pots will be UNSAFE for food use.
Also, like the others said, you will weaken the heating elements in your kiln.
Not cool.

Re: pottery in glass kiln

Posted: Thu Nov 13, 2014 7:32 pm
by Morganica
Repeating what others have said, mostly, but the vast majority of fusing kilns top out at 1800F (or even 1700F), so 1830 would be a stretch. And that is a bisque fire, most likely, so the second firing, where you glaze the bisque and fully sinter the ceramic, would need to be even hotter.

It's difficult to translate cone to temperature because they aren't the same thing--cone is an energy level, meaning that you've applied X amount of heat over a period of time. As Charlie said, you apply the heat long enough to make a standard ceramic shape (a cone) soften and flop over. They use that standard because ceramics kilns use different types of fuel and firing techniques to reach the same goal. accurately fire your son's ceramics, you'd want to get yourself some cones and holders for both bisque and final firing, and do some test firings to see if the kiln is capable of sustaining that much heatwork for the right amount of time. If it can't, there's no point in continuing.

If it can, you'll want separate kilnshelves for ceramics, because both the clay and the glazes can add contaminants to future glass firings. Buy ceramic (not glass) kilnwash and I'd strongly advise talking to the place that sells the clay for good firing schedules and other advice. Understand that you probably will accelerate wear and tear on the kiln pretty dramatically.

Important point: Fusers often fire in a studio garage attached to the house, or even inside the house, because glass firing off gasses are mostly harmless. That's not necessarily the case with ceramics, especially when firing glazes, so if you're going to fire glazed bisque in your kiln, make sure it's vented outside (or take the kiln outside).

Re: pottery in glass kiln

Posted: Thu Nov 13, 2014 10:58 pm
by charlie
it would be far better to obtain a cheap pottery kiln off ebay or craigslist, for all these reasons.

Re: pottery in glass kiln

Posted: Fri Nov 14, 2014 12:51 pm
by Judd
Good point Cynthia. Glazes release gasses that will kill you. Or, if not kill then give you wonderful diseases like pancreatic cancer, lung cancer... stuff like that. Always fire pottery kilns in well ventilated places.

Re: pottery in glass kiln

Posted: Fri Nov 14, 2014 7:15 pm
by Corlette M
Yikes! Thank you all. I think he'll have to keep firing at school for now as this is more than I want to learn. There's not enough time for glass as is. Thanks again. Happy weekend .