Slab Boxes made from flat pieces of clay

Slab Boxes made from flat pieces of clay are more prone to crack than most other clay forms. WHY DO BOXES CRACK? Moist clay shrinks a lot when it dries. If a box is on the shelf to dry, the bottom will dry slower than the top. This or other uneven shrinkage will often crack the box.

THE GENERAL PRINCIPLES Construct the whole box from pieces of clay that are all exactly the same hardness at the time of assembly. Generally, this means that some planning is required. When pre drying a slabs to be used for pieces of a box, wait to trim them to size until they have firmed up a bit for assembly. Trim away about an inch or more from all sides. Otherwise, some of the edges are dryer than the centers of the slabs. Cracks may show up later. Assemble the slabs before the slabs get leatherhard. Use clay that has firmed up, but while you can still bend it a bit without cracking. Otherwise, the slip added in joining can cause too much variation in hardness and subsequent drying shrinkage. Slip, water, and/or soft clay is added at the joints. This causes softer areas. Therefore, wrap the whole box in plastic several days before allowing any drying. This allows for the stress to even out before serious drying shrinkage occurs. Dry it in a way that allows the water to leave at the same rate from all surfaces including the bottom. The interior of the any box tends to dry slower than the exterior. This may have a tendency to develop concave surfaces. Counteract this by using slightly convex slabs and by drying the box slowly enough to avoid concave surfaces. Dry boxes on wire racks http: //www 2. goshen. edu/~marvinpb/dryingboxes. html

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• Problem that can arise is that the heart shrinks more than the box and the lid will not fit after firing. • Solution is to make the hearts have a gap from the box and to dry as one unit with a wax paper barrier. • Piercing a vent hole in the box and firing as a unit will also help.

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