Friday, May 21, 2010

Slumps, Bumps, Pits

My frost porcelain plate slumped and it has bumps. This was fired in the school kiln. I am told they fire to a hot cone 6. Debris fell in the glaze from somewhere and the plate slumped, not sure where it was located in the kiln. Oh there's a few pits in the glaze too. The companion to this plate is being fired elsewhere, the comparison should be interesting, stay tuned for that.

The good news is my experiment is a keeper. I put the black flower designs in slip on greenware, bisqued, then I sprinkled orange and green underglaze and then glazed with a clear over. I want the speckled colored glaze to be darker and more of them, but I like the layered look. I used a shiny clear, but I prefer my matt clear glaze much better than shiny. Next time it will be what I am striving for.

Here's a frost porcelain tray with a blue shino glaze from the school. Not a high fire shino that's for sure. I really miss high fire glazes. I didn't even notice the red color on the side till I took the photograph, looks like whoever picked up the piece must have gotten some other glaze on it. How do you prevent cross contamination of other glazes when loading, I am curious?

What cone should mid fire clay be fired to? The school fires to a hot 6; the woman who fired my last batch before I left California fired to a cone 6 with a 20 minute hold; the place I've taken my work to be fired this week fires to a cone 5 with a ten minute hold. Does it depend upon the clay, the glaze? There must be a rhyme or reason to firing cone 5/6.

Above is another glazing experiment being fired as we speak. In my packing I discovered a bunch of Mayco Jungle Gem glazes I had from bead making. I dabbed a bit over in various spots on this vase which is itself an experiment in embedded clay upon clay of the same type. I purposefully left some red clay showing. Some Mayco glazes will fire to cone 5/6; they have examples on their website of what they will look like fired.

I ordered my kiln; it should be here in about three weeks; more about that next time. Don't go away I have fifty more pieces coming up in the next week to show. Yes, fifty pieces, I can't even believe I made that many. Comments and suggestions are welcome.


  1. I'm lost as to the firing particulars (but am learning) but really like your flowers, the petals have a rich deepness. And your gray tray is to die for!

  2. The studios I have worked at all fire to ^5 with a 10 minute hold. I also fire to ^5, I soak at 1100f for 20 minutes and I hold at the top temp for about 30 minutes. The thing about using community studios is some of them don't clean the kilns out well and don't maintain the shelves all that well and stuff flies around and gets on your work. Some of them have old old kilns that fire inconsistently too. You will be much happier with your own kiln. Can't wait to hear about that!

  3. ^5 and hot ^6 are different enough temperatures/times to make a big difference in how your clay body reacts and what the glazes do. Some glazes won't melt properly at ^5 but are perfect at ^6. Some clay bodies will crack at ^6 but be fine at ^5.
    The red you see on the blue shino may be from the shino itself, shinos react differently to variances in temp, reduction, etc.

  4. Hi Linda! I usually fire to 5 with a 10-minute hold. But... I have some pieces I'm unloading this morning that I didn't "hold." I was having some slumping of the larger plates and I read that not holding during the glaze fire may help with that... We'll see. Lots of trial and error...

    Wow, 50 pieces! You've been productive.
    You'll be putting your new kiln to use soon!

  5. Hi Kittie, thanks, the platter is a little bumpy so not saleable, but I might make more rustic looking trays like this one. I do like the shape. It would be good for to serve little crumpets with tea or cheese and crackers for two. I'm going to make some more of the flowers with stoneware and try the same technique. I do like seeing the brush strokes of the slip decoration, showing that it is hand painted.

    Hi Tracey, thanks, that's a lot of holding, I remember your talking about it and that may be the way to smooth out the glaze. Yeah these kilns are pretty overworked and stuff is flying all around everywhere. the next place I've taken my stuff is a professional potter's and she will do a much better job I think, although her studio has open doors and dust can settle on the glaze till she fires it.

    Hi Lori, thanks, most of the students are using a stoneware clay and the frost porcelain is more temperamental. I will see how the next plate does in the cone 5 firing and see if there is a difference in the slumping. I think a lip or rim on the plate would help. I didn't think an electric shino would do that, but then again, I have had flashing on one pot from another in electric which might be what happened to this one. The color isn't separate from the glaze so it may be what the shino did itself.

    Hi Patricia, thanks, I have a couple of 16 x 12 platters that I should probably have fired with no hold.

    Yes I didn't realize I had so many pieces I made in the RV. I've made even more since we moved in and those are drying. Once I determine a group of pots I like and glazes that pass the test, I will then begin making multiples of those.

  6. Hi Linda, Nice results. Glad you're getting your own kiln soon. I usually fire the Frost to ^5.5 and it does well.

  7. Hi Cindy, thanks, seems there are lots of variations in firing schedules, I'll see how this next big bunch comes out that I am having fired. I got some stoneware and will work with that again and see how that works out too.


I love suggestions, questions, critiques, thanks for your comment