single firing, cone 6 stoneware glazing greenware and firing only once
Posted 09 May 2012 - 05:33 AM
I'm not a professionally trained potter -- I've been teaching myself through trial and error, and taking the odd class over the last year. I bought a used kiln and have had many adventures! Yesterday I was doing a glaze firing of some bisqued cone 6 stoneware pieces and I had a small greenware pinch pot of the same clay body that I'd forgotten to include in the bisque firing last week. I decided to glaze it as usual as an experiment to see what would happen if I skipped the bisque firing -- and then proceeded as usual for my glaze firing. The unbisqued piece appears to have come out exactly as it would have if it had been bisque fired first. It feels the same weight -- and the glazes behaved exactly the same as usual.This piece was glazed in the same glaze as a bisqued piece next to it in the kiln and their colour is identical.
So, my question is: what are the disadvantages of going straight to a glaze firing and skipping bisquing?
I can imagine that one hazard would be the effect that wet glaze could have on greenware -- especially a delicate thin piece -- there might be a risk of the clay disintegrating or cracking from the moisture. This didn't happen in this tiny experiment though (and I didn't even let it dry for long -- I glazed it at the last moment and just put it in the kiln and fired it up!)
I'd love to hear from properly trained potters about the disadvantage of simple single firing.
By the way - in case it is of interest in this matter: I have an old Duncan kiln that performs beautifully - although the kiln sitter does not work properly on a cone 6 firing (fine on cone 04 bisque firing) but I've gotten to know my kiln and it does a glaze firing in 6-7.5 hours. I watch the cones carefully and have had no problems.
Looking forward to hearing from the experts on this!
Posted 09 May 2012 - 09:31 AM
It's generally better to glaze the piece when it's leather hard, at least that is what the recommendations are that I have seen. I've done it a few times and like the way the items turn out. It's been a while since I've done any, but as soon as I get set up after our move I'm going to be making some bowls to single fire.
Posted 09 May 2012 - 10:18 AM
Never had major problems, sometimes I got bubbles in the glaze (to fast fire, to thick glaze).
Posted 10 May 2012 - 07:43 AM
If you are glazing bone dry piece you really have to be careful not to get too much water into it... so for example really thin porcelain cup cannot be glazed bone dry (at least with my skills)
Anyway if I would brush my glazes on, I would choose single fire.
Posted 10 May 2012 - 08:16 AM
Congratulations with trying and having success, and not blindly following accepted habits !!
I am very interested as well in single-firing and low temperatures- It saves electricity, saves the environment and saves time.
I think we can adapt techniques and glazes to accomodate single firing.
We should definitely not do bisque-firing simply because it is the accepted way of doing it.
E.g. bisque does make the work stronger to handle, but if we handle things more carefully then there is one reason less to do bisque,
another reason is that we do not always dip-glaze - we do not always have to.
I am very interested in other people's experiences with single-firing.
Posted 10 May 2012 - 09:52 AM
For my next foray into single firing, I fired a whole load of pots using the bisque up to red heat, then the glaze firing finish. No problems. I think the biggest issue may be firing out organic matter and having the escaping gas mess with your glaze. Going slow through certain heat ranges may help with that. I documented my first full single-fire load here:
My procedure for glazing is bone dry work, pour interiors on more closed forms, then spray the exterior right after. For open forms like bowls and platters, I spray the underside first then the top side. I admit that I still bisque then glaze most of the time, but my excuse is that I fire raku almost as much as regular glazed work, and single firing raku isn't going to work out.
Posted 10 May 2012 - 09:56 AM
i have been single firing to cone 6 for years but i spray my glazes so it is easy to apply glaze to greenware.
the best reason for bisque firing that i can see is that if you want to scrub on underglaze colors or glazes into deep textures or any other technique which requires a lot of handling of the pot before putting it in the kiln. my latest work involves textured slabs formed into flowerpots or vases. spraying an interior glaze into a deep pot requires skill and is not always successful. i have dozen water-filled vases sitting on my work table right now. they have been there overnight to test their waterproof quality. one didn't make it because my spraying missed a small area near the bottom of a 7 inch deep vase. having poured the glaze into a bisqued vase would have avoided that one problem.
the strange thing you will eventually learn is that there are no absolutes in clay. someone's comment about bisque being stronger seems reasonable and i believe it. BUT. last week a phone call interrupted me while i was pouring glaze into a deep bisqued (to cone 04) vase. i got distracted and the vase was sitting there with a totally wet bottom half (6 inches) when i got back to it a few minutes later. after pouring out the glaze and finishing the exterior, i put it into the kiln. during the subsequent firing, it deformed in that area and the exterior glaze shivered off in a long, narrow section. go figure.
Posted 10 May 2012 - 10:16 AM
And "oldlady" (I don't like calling you that!!!) your comments about there being NO constants is well received. There are so many variables, as I have learned, often the hard way.
But in the end, it's only mud and water, isn't it? You can always try again. Although it never turns out the same, the next time!
Posted 10 May 2012 - 10:34 AM
I fit that description- One thing I should say first if whatever works for you than by all means do that-There is no right or wrong with clay. Some things are easier or harder.
As far a single firing from my point is its a slower glazing process with some risk of loss it lends itself to spraying the outsides. As a production potter I am all about the speed of production-we wax with a sponge (I can cover this later as well as hot dipping paraffin) The glazes are brushed and dipped not sprayed which is a slower process.So on speed and loss I'm bisquing. But if speed and efficiency do not matter by all means single fire this will be true for many hobby potters. Our USA salt history of pottery is all single fired and it works well on liner glazes. I single fire some salt wares myself. But of all the production potters I know in my art world none single fire. A few other considerations are stacking bisque ware for storage -with green pots this is limited. I stack bisque a mile high and stockpile it. Breakage is nil. Green ware is fragile so loss happens.
Hope that helped-I do many unconventional things and I think there are no rules is a good one.
Posted 10 May 2012 - 04:12 PM
q: MarK C, can you tell more about sponge waxing and parafine dipping?
Is this pure parafine? mixed with wax? I have seen parafine dipping on youtube and it seems so easy
which pots do you dip and which get sponged?
Posted 10 May 2012 - 04:20 PM
I just made a whole whack of pendants -- I can see how they are perfectly suited to single firing -- they are flat, and can be brushed easily and quickly. I'm also going to single fire a whole kiln load of small pinch pots - the kind I sell as salt cellars. I'll glaze them at the leather hard stage. We'll see what happens. I'll have the usual trepidation opening the kiln!
Posted 10 May 2012 - 06:32 PM
With simple glaze work I feel that I could be a raw ware production potter but It would effect shapes and workflow. I belive I would save time equal to the bisque. I think you can raw glaze most things if you get the timings and techniqe right but that takes time to learn. Another problem is the need to dry the pieces evenly, before dipping and after as glazes tend to flake if they dry to fast in the stage when the pot changes color; this will take some extra managing if you don't make some special drying space - not to dry, not to cold. But it seems like you have a super glaze there.
Another feature is that I can rawglaze my work at home, bisque it (!) and trasport it, glazed, trouble free. (I use a lot of different kiln over the country.)
Posted 11 May 2012 - 08:12 AM
I have done single fire twice now. Seems to work great. Got the idea at one of Steven Hill's workshops.
Only problem so far... pieces break while glazing .... need extra care due to fragile nature of the dried raw clay.
As far as the firing itself - There is a low candling at first then ramp it up. I think there is a ramp setting on Hills web site. I modified it for my glaze. If you would like my temps and time let me know
Posted 11 May 2012 - 12:08 PM
In my opinion, the major risk with not bisque-firing is having moisture trapped in a glazed greenware piece and having it blow up in the kiln. That can ruin an entire load, and also be really hard on the kiln. However, if you're careful to vent any enclosed sections of your pieces and thoroughly dry your work, that shouldn't be an issue.
Posted 11 May 2012 - 12:55 PM
I pour the insides of the pots and spray the outsides. I find the time (and energy - both electrical and personal) saved through eliminating bisque firing is well worth the extra care necessary in handling the pots. And I agree with StefanAnderson - if you're into heavy production, you might not want to risk the possible breakage. I am converted, just working carefully so I don't run into problems.