I have a piece I have spent hours on. It is now almost bone dry, though I am holding it back. It is showing small cracks at the bone dry stage. What should I do so the cracks don't make trouble for me???
Marianne
Hi Marianne, If the cracks are small do not wet around the crack - just rub some dry clay dust from surrounding area with your fingernail or wooden tool. If they are big - paperclay is a good solution - but don't wet it too much as it will shrink as it dries ( original clay piece, not paper) and it is likely to show cracks again. Try simplest solution first :o) good luck, Andrea
One thing I learned about cracks and their prevention is to carefully control drying of pieces that have a lot of different features -- specifically thicker and thinner parts. The clay shrinks as it dries, and shrinkage is generally a function of size. If one part dries faster than another part it is connected to, then it is likely the drier part will pull away, opening up cracks.
Most here know I am certainly no expert in this, having just taken it up. However, for what it's worth, I found that covering a piece I've done a lot of work on (a handbuilt piece with different kinds of parts rather than a thrown bowl, for example) with dry cleaner bag plastic for a couple of days allows the clay to equalize moisture throughout. Then, I cover it with a plastic bag with several snipped scissor cuts so it can begin to dry slowly. It might remain under the snipped bag for several days. Then, when it shows evidence of surface drying (chalky surfaces) I uncover it and let it air dry from there. So fay, the process has worked pretty well for me (knock on wood)...
I'm fairly new also, but I'll put in what I've learned (or should have). If you are talking about plates and wide bottomed bowls, to prevent the dreaded 'S' crack in the center, use a LOT of downward force when first spreading the clay outward on the bat or wheel. Another thing you can do that I learned from the lady that sells the 'Pure and Simple' mold system is to first make a 'pizza' dough shape by hand rather than centering and pushing down the clay.
Tom
As the piece wasn't bisqued yet, I actually just wet it more and more, packing it in plastic to even the wetness. When it got to the stage where I could add clay to it again, I did just that at the cracks (two nasty ones from the edge of the lid, going up) and then used my triangular knife to blend the new clay with the old and then smoothed it all out again, and kept it wet for longer and packed it in plastic so it dried much more slowly after. The pot is now both bisqued and glaze-fired, and the cracks are nowhere to be seen. Phew!
Marianne
Hi Fred
Yes - that was what went wrong for me with this piece. I had opened it up to let it have a bit more dry air, and forgot to close it before it dried too fast, and thus the cracks appeared. See my other answer on this thread for how I solved it.
One thing I have realized over time, is that it is a smart idea to put newspaper between the plastic and the clay, as then any condensation will be spread out by the newspaper, and not drip or collect in just one spot on the piece.
Marianne
InspirePoint website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.