Question- what causes this crack? Is it from the bottom of the bowl being too thick? or uneven drying? or not compressing the bottom enough? What???
Wisdom please!
Am back from time in Costa Rica. Good trip, although so exhausting! I'm happy to be back home. Soon will be working on new forms- first to finish a few orders.
Thanks for reading and your comments.
8 comments:
I've heard those types of cracks are because not enough compression was done during the throwing but I've gotten them with slab built pieces of mine; now I dry all my work on sheetrock and if the piece is thick I move it from one sheetrock to another twice a day for a couple of day. I set the sheetrock on an open weave shelf so air can circulate from below. When firing large flat pieces I use porcelain sand under them so they can move during firing.
If it goes through the pot It's definitely an 'S' crack. As Linda said, they are generally caused by not enough compression when opening up. I just dry stuff slowly and evenly. Did you see any indication of a crack in the bisque?
Of course this my remain one of life's little mysteries!
Sounds like you are well aware of what to do and what not to do. Sometimes it really is a mystery. I've been using the sheetrock/drywall too, like Linda mentioned. I asked a contractor who has done work for us for leftover pieces. If you want to try, the way to cut is score the paper side with a utility knife. So I make one long score then bend along the score line and it will snap easily. Now I have one long piece which I will score and snap horizontally. Wrap the edges of the square/rectangle shapes you just cut with tape- masking, painter's tape, duct tape. A wide width tape is good. You just don't want the crumbly drywall getting in your clay.
Hope I'm not telling you stuff you already know, but in case you don't, the drywall really does a good job drawing water out of the bottom of your freshly thrown pot.
I dry my bowls on non porous boards, theory being that the clay can shrink evenly. Also, a lot of times cracks happen because of uneven thickness of the bowl, it will crack in places that are thinner, or places that are thicker, again it's all about even drying and clay shrinking. Having said this, these suggestions came from a teacher long ago, and I have never had a crack in a bowl, except from harsh raku firing.
Thanks, all. Yes, smartcat it showed up at the bisque stage. Saw one of them before it dried completely. Yes, it's an S crack, I think.
Tracey- what do you mean by a non-porous board? a wood board? What's an example of one? This visual learner is trying to imagine what you're saying...
Melissa- wow, what you said is all new news to me. Any pics to help explain? just set it on drywall pieces?
hmm...
Hi Amy,
I can see that you have been given great advice regarding the crack in the bowl. You can probably get the answer to just about anything from other potters that blog, which is wonderful, but... one book that I find really helpful to have in the studio to consult when things like that happen is "The Potter's Dictionary of Materials and Techniques" by Frank Hamer. It is a big book, and may look a bit technical, but it is a surprisingly good bedtime read and has some very useful photos and drawings.
Thanks, Peter! Will take a look at that book.
Non porous- melamine particle board or vinyl laminate. I found some boards, probably old kitchen cabinet shelves at the habitat home store for $1 a piece..... I like them because they clean easily, won't warp, and don't fall apart like Sheetrock eventually does from the moisture. You will see them in recycle stores usually white, I imagine Lowes or Home Depot has new ones but I like to buy recycled when I can....
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