Nice Bottoms?

[Carl Stewart]

OK...I've fired salt a few times...but several years ago was the last time. I was getting some wonderful results...nice pinks and orange blushes on a light clay body. I'm starting with another kiln and mixed up the same clay--it's got quite a bit of grolleg in it...some molochite, Hawthorne, ball...I don't have the recipe handy. A few tests suggested that I had the claybody back.

Well, I fired practically a whole kiln load and...ouch...blah, got a lot of oatmeal. Some flashing slips (smooth orange from here, EPK and Grolleg and Nephsy gave some relief...but way too much oatmealy pots--the bare clay body.

I was thinking about it, trying to figure out the issue. I fired to just cone 9/10, a clay reduction then pretty oxidized on up as is the tradition with this kiln. Packing up the pots, I continued to admire the bottoms--the bottoms had the oranges and pinks....

So this is the way I am thinking: I used too much salt (and yet I was lighter than is traditional with this kiln). I took rings out before I salted and there is plenty of residual salt. I think I am going to cut the salt by about half. Do you think this is good thinking? What is going on under those pots between the wadding? It's getting less salt, right? My surface was generally more glazed, wet that previously if my memory serves--that's the give away. Yer comments and suggestions are welcome! Sorry, no pix yet, but you get the idea, right?.

[June Perry]

Could there be a change in the your clay body ingredients? When the silica alumina ratio of a clay body is under 3, the body will flash. When you get above that 3 ratio you can start losing the flashing. If you've changed some ingredients or if the formula of one or more of the ingredients has changed, that could possibly be enough to alter the silica alumina ratio.

Too much salt could be one of the problems. Are the fuels the same in the old and new kiln? You might want to check all the variables, i.e. are you using the same firing schedule, reducing at the same times, with the same amount of reduction, etc.

June
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[Carl Stewart]

Thanks. So if SiO2<=1 and Alumina is 3 will flash. So flashing slip like 75 grolleg and 25 Neph has that since it flashes?

There are a lot of variables that I just don't know about--like firing schedules etc. But both were gas kilns.

[bryce brisco]

i would think you need to add more iron to your clay body, try a small addition of Red Art +/- 5 %, Newman red, Helmar, etc...as far as the wadding goes, check out the calcuim carbonate discussion, or see the article about active wadding in the recent ceramics monthly, also try firing on shells for fuming...good luck, bryce

[Carl Stewart]

Thanks. These suggestions seem reasonable. I had seen the disussion of CaCarb but hadn't read it until you pointed it out. I'll fire this kiln again in May I think. It has also been suggested that I do some conscious very tight loading to create the kind of "tight confined atmosphere" like there is for the bottoms of the pots.

[Scott Cooper]

Hi Carl,

I understand the suggestions to revisit your clay body recipe, etc., but it sounds to me like you're getting the effect you want with the current clay -- just not where and how much you want of it. I think exploring the tighter loading option is a good place to start, because it's such a simple variable to change, and you could try a lot of different options in the same firing. Trying less salt also sounds good, but I don't know about cutting it in half -- that sounds like a pretty extreme change. (I guess it depends on how much you dislike what you have now vs. how willing you are to take a bigger risk.) I try to be somewhat cautious and change one thing at a time, but it can be hard to have that much patience...

I often like the bottoms of my pots too, particularly where the vapor flashes past the wadding. I'd think about stacking in a way to create similar tight spots that shield one part of the pot while channeling the flame and salt elsewhere. Or perhaps stacking vertical pots on their sides or tumble-stacking part of the load, so that the pots shield each other? As with changing the amount of salt, I'd try this in moderation, also -- too much of that sort of thing could block the path of the flame and slow kiln, or create new cold spots, etc.

Just my 2c.

[Carl Stewart]

I don't think I ever replyed, but I appreciated your comments. Firing again in a week. I've made some forms to really do some serious shielding....and I will take your suggestion to not be too radical in my reduction of salt....see the next comment.

[Colleen Riley]

Did you say this is a kiln you fired for the first time? If so, my guess is that since your draw rings looked glassy before you added the salt, you may have a LOT more residual salt in this kiln. This, combined with adding more salt, probably took your surface past the point of flashing and to the point of creating a glazed surface on your pots. Different bricks and coatings absorb more or less salt, so it's possible this kiln just has a lot more salt to give back.
I'm not sure if you're going for more traditional salt effects on your pots, but you may consider adding soda. Soda, combined with the residual salt in the kiln, might give you really lovely flashed surfaces.
The grolleg/hawthorn/ball clay body should flash nicely without much help from slips....but you definitely need a fair percentage of hawthorn and ball clay to get the grolleg to do anything. And, as June suggests, the newly mixed clay body may be fluxing more than you're used to (not enough alumina).

[Carl Stewart]

There is definitely a lot of residual salt...from the draw rings I pulled prior to salting. Firing next week and will let you all know....and try to get some pix up too. Thanks!