A: It depends on the type of application, process and end result. As a general rule:

  - Earthenware clay (eg. Terra-cotta) is great for sculptures and ornamental work. Also great for outdoor planters. Its a low firing clay so it isn’t vitrified (non-porous) so it wont be sealed unless glazed all over. 

  - Mid-Fire clay can be used for functional ware (plates and cups etc), sculptures and ornamental work. Some Mid-fire clay is vitrified.

  - Stoneware clay and porcelain is a high fire clay and is suitable for functional ware (plates and cups etc), sculptures and ornamental work.

  - Air Dry clay doesn’t get fired in a kiln, will be porous and cannot be used for much other than ornamental work. You can paint it with acrylic paint and seal it. But it is not safe for food or water. 

A: If you use a low fire clay, you must use a low fire glaze. If you use a high fire clay you must use a high fire glaze. Clay and glaze need to “fit” each other when they get fired in the kiln. Putting the wrong glaze on the wrong clay can result in the glaze melting off the work or the clay melting under the glaze. Either way, it won’t be pretty - imagine trying to spread buttercream on jelly. It would just slide off - they just don’t go together. Glazes have different ingredients that react differently to each clay. Some look amazing, some look brown. 

Here is a good tutorial for glazing: Glazing

A: There are so many reasons why work cracks. It is hard to determine the cause without examining the piece or seeing the making of it. One possible reasons is that it can happen when joining pieces together. Joining cracks happen when one piece is dryer than the other, or dries quicker than the other. It can happen during the making of the work but is only evident once it starts to dry out. The best way to avoid cracks in your hand built work is make sure the clay is at a workable (plastic) state and not too dry. Make sure that if you’re adding pieces like a handle or a foot that you use the scratch and slip method and that each piece has the same moisture content as the rest of the piece. Wrap the work in plastic so that air can get in but the air is slowed down, giving the work time to slowly dry out. 

A: I use a combination of cement sheeting and marine ply. Both are porous (clay won’t stick to it) and the board makes it easy to lift work without deforming it. I have a few A4-A5 sizes for working on and some larger A1 size pieces for drying and transporting around the studio. 

A: Once work is bone dry (no longer cool to the touch) it can have its first fire. You can pack greenware (unfired work) in a box with corn starch packing beans or wrap carefully in bubble wrap or old towels. Greenware is delicate, don’t grab it by the rim! Glazed bisqueware is still very delicate as some glazes turn to powder on the surface of the work. Transport with care.