Thursday, September 15, 2011

Parallel Lines

As I was looking at the pieces that warped during the two once firings, highly disappointed, I was thinking how I like the slip colors on the white clay, but I also like the slip colors on the red clay. So I have to find a way to get the red clay to work. Maybe not this red clay, but some type of red clay.

The red clay seems to change the look of the slip colors warming them up and I like that look. I also like the crisp look of the white clay as the backdrop for the slip colors. I was looking at the pieces made from the white clay and wondering what each one of them would have looked like with red clay and visa versa. So for now I'll be working on parallel lines of work, one with white clay and one with red clay.

Do you know what caused this strange swirl mark on the back of the clay. Gary said it looks like a smoke pattern burning off. During the first once fire I fired the red clay pieces upright and they slumped in the middle and warped. So in the next once firing I turned them upside down and fired them with the slip side on the kiln shelf. That's when I got these swirl marks. Oh I just noticed the swirl marks are only one one type of red clay the other clay is more of a brown and it doesn't have the swirl marks.

Today I was wondering if the swirls could be from how the clay was mixed. I use the clay straight off the slab and then roll it out in several directions. I wondered if the swirl mark could have come from some of the clay not being mixed, but that doesn't seem possible. Surely the clay is mixed better than that before it's shaped in the blocks of clay at the factory. Could they be just about ready to crack in that pattern, they don't seem to be weak in any way at that point. Any thoughts?

Here's one that didn't warp too bad and was fired upside down, but some kiln wash stuck to two of the dots and I've been trying to sand that off. See what I mean about the red clay warming up the colors of the slip. The rest are photos of the warped pieces.

I think the warping may have come from how I dried these pieces I had them propped on some soft foam and they may have retracted trying to shrink and that caused the stress in the middle. Better luck next time. Thanks for reading and for all your comments.


  1. Hello Linda:
    Well, we have no answers but, although disappointing for you, we are learning a great deal about the trials and tribulations of pottery making.

    The clay colour does make a difference to the tints and tones of other colours used and it is an intriguing conundrum to decide which is best.

  2. Hi Linda. I am not a slab expert so no advice there.You know I like red clay and letting some of it show. The parallel pots sounds like a good theme.

  3. Hi Linda, Like Dennis I don't work often with slabs and when I have, I fire flat sheets with high firing sand underneath so the piece can move as it shrinks. Perhaps the swirl could be some extra iron oxide in the clay that built up as it was prepared at the supplier if there is no weakness there.

  4. Don't count on the supplier mixing the clay well. I've sliced into blocks that have a center 'square' of one shade, and a 1-2" border of another around the outside.
    I'm a thrower, so I always wedge anyway, but annoying.
    If you make a careful slice with a smooth wire, can you see any swirl on the raw clay?

  5. Hi Jane and Lance, thanks, and sometimes it's hard to decide which color ones likes best, part of the fun of it though.

    Hi Dennis, thanks, yeah the earthiness of the clay is part of it's charm.

    Hi Anna, thanks, normally I use high fire sand underneath too, but this time I didn't to no ill effect.

    Hi Brian, thanks, I didn't notice any swirls when I cut into the clay, I'll look more closely at that. After I cut the clay I press the thick slab down with my palms then I roll the clay in several different directions till I get it to the thickness I want before using it, flipping it over after each roll, so you would think that the ingredient would have distributed. It will be interestng to see with some other pieces I have made, if the same thing happens.

  6. i don't have any insight to the swirl but i am wondering if your tiles were thicker, since they are quite large, you may have less warping. that sure is some serious warping, so disappointing after you put all that work in the slip application and carving.

  7. If this is Cone 6 clay fired to cone 6, could just be that the clay can't hold up with that thinness being fired right at it's maturity. Thicker slabs as Michelle suggested? Maybe try firing a bit lower? Maybe try using Cone 10 clay fired to Cone 6? It's more work, but maybe slab side supports of some sort?

    Think the swirl is just from the mixing in the industrial de-airing pug mills the clay companies use. @Brian -- hope you called them - that should never happen. Clay company I used to work for had a really cheap clay called "gumbo" that was the clay that came out between batches. It was always a surprise in every bag, but people expected that :)

  8. I've dried tiles very slowly on a baking rack so they get air on all sides. For non-tiles I still like to dry them on a towel or old t-shirt on a wire shelf, it may help cracking too.

  9. Hi Michele, thanks, the tiles are 1/4 inch after firing. I didn't want to make them too thick since they are to hand on the wall. I actually had more cracking when I made them thicker. I may need to find a happy medium of a little thicker but not so thick they crack. I had a bunch warp, but I also had a bunch that didn't and so many good ones, it's not so diappointing.

    Hi Barbara, thanks, the swirl pattern is so even I think it must be some of the ingredient that didn't get mixed. First time I ever saw that. I didn't call them cause I just noticed it this week and wondered what it was. This wasn't supposed to be any gumbo, it's Laguna WC 601 #30, supposed to be Cone 6 and ideal for hand building and sculptures. I've used it before and never had this swirling so it may be a fluke for just this time. I may see about using WC 614.

  10. Hi Lori, thanks, I am drying these on wall board lightly covered for weeks inside my home. I've been having pretty good luck with no cracking once I made them a little thinner. None of these cracked and I think the warping was because of the way I dried them on foam. I used the foam because I wanted the sides to curve around the wood backing I'll be putting so they can be hung on the wall. I may need to improve that drying method and it will straighten this warping problem out, because the flat ones do just fine.

  11. i was so intrigued with your swirl that i asked jeff to look at it. his first question was do you wedge your clay before making your tiles? his theory is if you wedged your clay and rolled it out with the "rolled" ends of your clay on the top and the bottom as opposed to laying it on it's side (rolled ends to the left and right), the swirl came from that. he also said that may have played a part in the warping. he also agreed that thicker slabs may help.
    i am not sure if i was able to put that into understandable words!

  12. Long ago, I took a class where we made chunky wall tiles by joining stiff slabs around the edge and building a + structure inside to support from warping, but I really love the way yours curve. Maybe you could make some sort of supports that would go under the tiles while firing?
    @Barbara, yeah, I would have if it was my studio, and I had purchased it, but alas, I work in a community studio. I did take note, however, for the day I'm buying my own clay.

  13. Hi Michele, thanks, no I do not wedge the clay. I cut a very thick slab from the block of clay straight from the bag. I press it down with my palms to about 3/4 of an inch and then I begin rolling it, roll one direction, flip it over, roll another, flip it over, I rotate which direction I flip it over till I get it to the thickness I want. Then I take rib and compress in two or three different directions. I'll try to go thicker next time to see what happens. Thanks ever so much. These were on lower shelves and not much space between each shelf and since they were upside down I was thinking the outgassing might have had a hard time escaping being trapped within the sides, but the swirls are too even for that so it must be the way the clay was initally mixed. I will check with Laguna and Bennet's. I have always made my slabs of clay this way even high fire and have never had this kinds of swirl before.

  14. Ok I just re-looked at the cones. The cone 5 fell back and hit cone 6 underneath which may in turn have propped up cone 6 which might mean that cone 6 would have fallen over lower if cone 5 hadn't held it up, which would mean that it may have fired a little over cone 6, which may mean it was a little too hot. I looked at the cones for the other once fire and the cones did the same thing, touching or kissing and holding each other up. So I will adjust my firing schedule for the next once fire and reduce the hold time by five minutes to see if that makes a difference. I will also start taking a photo of each cone pack when I fire so I can compare them. Since initially I didn't notice the swirl marks on the tiles till after I really started to look at them.

  15. me typing for jeff again... since you didn't wedge it is most likely the swirl from the pug mill at the factory. he suggest cutting a slab vertically from your tube of clay and see if it eliminates the swirl.

    me again... was your cone 5 facing the wrong direction? do you use self standing or make cone packs? we make cone packs and i am always fearful of putting one in the wrong direction. i double check them by standing them up and knocking them over to see where they fall even though i know if the numbers are in the right direction they will be fine. i think it's an OCD thing!!
    on another note... we fire to ^10 but always put a ^11 so we know if we have gone too hot, although most of our glazes are ok at 11.

  16. Hi Michele, thanks, the cones are self supporting, but I put them on a hard pre-made cone stand, but some how it leaned backwards. I probably need to put a cone 7 in the next firing to see how it does. The self supporting cones already lean in a certain directing and I always make sure they are leaning the correct direction, but somehow it hasn't worked the last two times.

    Perhaps the additional heat was because I had two half shelves and posts in the load and that added to the overall heat of the load. I will try slicing off the clay a different direction next time to see how that affects the outcome, good idea, thanks so much.


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