How to prevent cracks
Planning: Porcelain dries faster than other materials than I have used before like raku or phoenix and if you go thinner you need to be even more careful. I agree that you have to play with the material to know its proprieties first then you have to realize that everything is possible if you make a plan. Sometimes we concentrate on what we want to do, but we don’t have a plan on how we can do it. Is the piece going to involve carving? Does the piece need structure? What support material do you have to make, if the structure that you are going to use is like foam, does it let the clay dry is at the same time?
Work surface: If you choose drywall to use for your work surface, remember to put duct tape on all borders. The drywall has plaster inside like you see below in the picture , if these particles mix with the clay, they can be the cause of a blow up.
I made this frame for a mirror using porcelain a couple of years ago, it was my first piece using P10. In my head I had a vision of my piece, but I didn’t plan so well how I was going to make it.
Because I had the studio far away I had to transport the piece. I used a thick piece of wood for a work surface and I used a thick black plastic, in the center I used cardboard to cover the space for the mirror. I learned that using wood without plastic is not good because the wood absorbs humidity from the clay. Thick plastic is no good either because it doesn’t dry at the same rate as the top, the clay is much better to dry at the same rate; top and bottom to prevent cracking. Delicate pieces are much better to make on top of the kiln shell, that way you don’t have to lift it.
Time: I found out it is very import to estimate the time it takes you to make the piece not only because you would like to track the time also to choose the type of plastic to cover the piece.
I carved all the corner figures without covering the frame with plastic. All the borders started to crack and warp. I solved this by covering with wet paper towel for one day.
I found out if I don’t have too much time in the same week to work on the piece you can cover it with wet paper towels, (the best is Scott 55 , you can find it at Home Depot) then you can use plastic Press’n Seal from the kitchen, because it is sticky so you can seal all the corners.
Using the right tool:When you use the slab roller: be careful with all borders, all the cracks will try to continue, pressing all borders helps. To prevent bubbles you can use the pinch tool to open any bump.
Knives: Remember, a line made with the knife in porcelain will try to continue creating a crack. Rounding all the angles helps, you can use a wet makeup sponge rubbing very gently or use a very thin brush. Turning the knife before crossing the intersection of two lines helps to prevent cracks, the same movement that you use to turn the pencil when sketching or drawing.
Sharp tools: It is very efficient when your tools are sharp especially if you like to carve. Unfortunately you can leave a mark that creates cracks when you use a dull tool.