The S Crack

There's something that happens to wheel thrown pottery that can completely ruin a piece without you ever laying a finger on it. The S crack. It's something I had been battling for a long time. You make a beautiful little cup, and are sure that it's perfect, you leave it to dry nice and slow, only to find a few days later that the bottom had cracked in the form of a S. Sometimes it cracks all the way through the piece, or maybe its just a little hairline split, but either way it's ruined.

Four years later and I'm still having that S happen!

 

While known as the S crack, it can sneak up on you in a variety of annoying cracks.

I had thought that the S came from too much water collecting at the bottom of the cup while being thrown. In high school we cut our pieces off the wheel, which I guess eliminates the S problem since a bit of clay stays behind on the wheel. My teacher had never mentioned the S, and I don't recall my aunt, who first taught me pottery, ever mentioning how to remedy this problem. Yet it continued to happen to me quite randomly whenever I was throwing pots.

Leafing through the book The Ceramics Bible, I came upon the answer! All you have to do is "compress the base with your thumb to prevent an 'S' crack from occurring". Something I had never paid too much attention to because I tend to naturally pull out a pretty flat bottom. But by simply going back over it a few times with your thumb or a sponge, it can align the clay so that that all the particles are cylindrical. You can actually feel the clay aligning under your fingers.

I also came upon this little article, which had some other ideas if you're still having the S crack problem.

http://www.ceramicstoday.com/articles/103000.htm

For a little while I had been trying to keep the spiral pattern from wedging the clay aligned with the wheel, but really, it didn't seem to help as much as just pressing the bottom of the bowl right after I pulled out the initial shape. In that article the potter also suggests its a problem from too much water left in the bottom, so I guess my previous assumptions were correct too.

So remember, sponge out the excess water, compress the bottom a few times until you feel the clay align, and let your pieces dry nice and slow.

It's good I finally learned this, since I'm trying to go pro. It's never too late to learn a new trick!