Friday, February 11, 2011

Different Strokes

"Really? You can do that without adding slip and they stay attached?"

"You're kidding. If I try to do that with my clay it would sag for sure."

"You cool your kiln how fast?"

Those sound like bits of conversation likely to be overheard whenever a group of potters gather. Pottery, for all its "scientific" and technological advancement, still proceeds with a great degree of intuition, guesswork, and downright magic.

Much of this is simply because of the inherent inconsistency of working with constantly changing materials that are dug from the ground and processed by less than perfect means (and then mixed and delivered to us by low-wage workers who care a bit less about quality than they do about quitting time).

But I'll bet that we all know some potter who gets away with the seemingly impossible. We all know potters who have developed a method -- or series of methods -- that we're pretty sure we'd never be able to get away with in our own shops.

It's why potters sharing information isn't just a nicety. It's survival.

It's also why I don't usually file information about processes into files labeled: "correct way to _____", and "incorrect way to ______". No, I tend to file information in files labeled: "a possible way to _______."

It is with that in mind that I mention an interesting coincidence that has occurred in just this past week. In just this past week alone I have seen the mention of S-cracks (in the bottom of pots) brought up 3 times -- once in a blog post, once in a youtube, and once in an instructional DVD.

What's more interesting is that two of those mentions were of processes that that particular potter uses to avoid S-cracks ..... and neither one of them agrees with my approach.

The first approach was one I saw in a short youtube. In the video, the potter throws and centers the clay, then cuts the centered clay off the wheel and then throws it back down on the wheel head -- topside down this time.

The second approach was discussed in an instructional DVD. Here the potter says that he takes either the extrusion as it comes out of the pugmill, or the ball of spiraled clay -- the spiral being the result of hand wedging action -- and he then throws the ball of clay onto the wheel head, making sure to keep the spiral (created either by the pug mill or by wedging) so that its vortex is the center of the wheel head.

Me? ...I do exactly the opposite from the guy in the DVD. When my clay comes out of the pugmill, I slice the clay to the usable size, and I slap the clay into a shape just shy of spherical so that I can always keep track of where the pugmill-created spiral is. I then make sure that the center of the spiral is parallel to the wheel head.

I started doing this because I noticed (and you can experiment with this yourself) that if I ever take a very short, coin-shaped extrusion from my pug mill and just allow it to dry, that dry coin-shaped clay will quite often (if not always) develop an S-crack right where the spiral has trained but not quite joined the clay.

Therefore, I concluded, if I slam the side of the extrusion onto the wheelhead when I start to throw....sure, I don't (in theory) have the particles aligned for the easiest first pull possible....BUT, I do have the particles aligned along the pot's eventual bottom in a way that insures the fewest possible fault lines along which a crack might develop. And as for the particle alignment for throwing -- that all occurs during the centering process anyway.


  1. A possible way. I like that. I remember someone, maybe a teacher, saying there were as many ways to do things as there were potters. I've never tried any of these methods described to avoid "s" cracks. My own possible way falls into the "compress the bottem compulsively" camp :)

  2. John we wanted to thank you for posting the video of you putting the slip trailed vertical lines on your pots a while back. We tried it yesterday and it's so cool.


  3. Thanks for all your hints and especially the videos!!! They are so helpful and I too am wanting to try the slip trailed vertical lines. But I'm wondering how you color the slip?!? This is all new and I'm learning as I go, needless to say.
    Thanks, Debbie

  4. I do as createnicks says, compress the bottom, generally using a wooden rib. If nothing else it makes a smooth easy to clean surface.

    There has been a thread on clayart about S cracks too!
    If I had a pot that had S cracked I wouldn't keep it! That is being too precious.

  5. YOU GUYS COMPRESS THE BOTTOMS?! That's just wrong. Heh.

    I've got a couple of pieces around here with vertical feathering. I'll have to get some images and post a little more about it.


    as far as coloring the slip goes: There're endless possibilities, but an easy place to start is to create slip from a dry mix your own clay body minus any grog. If you don't know the formula for your clay, another approach is to liquefy some of your clay and screen any large particles out of it. Then, simple colors to start with are 5% red iron oxide (red brown), 2% cobalt oxide (dark blue under transparent glaze, but medium blue under semi-matte). 10% of any mason stain is a worthwhile experiment as well.

    Somewhere along into the few years and hundreds of pots I was producing of this kind of work, I discovered the visual impact of using white porcelain in conjunction with the stoneware slips. The added contrast made the patterns POP like nobody's bidniz.

    You'll also find that, as improbable as it sounds, the colorant can make the slip flow differently, so experiment around with those effects too.

  6. I compress only because that's what I was taught, but I only get s-cracks when I dry them too fast.

  7. I was taught to compress the bottom of my pots... which I always do, but somehow still come up with some s-cracks. Quite by accident I found the way that John describes and it really works!!! amazing.

  8. My take...I too have seen that if you take a "pancake" of prepared clay and bend it, you can see the auger spiral from the pugmill. This will cause theory, that the friction of the clay passing over the stainless auger blades causes a lot of heat to develop, making steam of some of the clay water at the point of contact, which doesn't bond together completely with the compression of the narrowing tube at the end of the mill. So, when I wedge, I wedge the clay in two directions, to mess up particle alignment, and when it goes on the wheel, the spiral should be perpendicular to the wheel head. Works for me, but then, I mash the inside centers of my big pieces with a 2 x 2 the next day and then reprofile the bottom, to get some serious compression. Best to you, as always, my friend! And, whatever works...

  9. I think spiral wedging is causing my s cracks I'm going back to slamming