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Picture a cross-section of clay with large particles of grog added. First, the grog opens the body to enable the clay to dry more evenly. As a piece of clay dries, the water on the surface evaporates. Water from the interior of the clay then migrates to the drier surface and, in turn, evaporates. Adding grog aids in this process by creating pathways for water vapor to move from the interior to the surface. Grog also helps control shrinkage. As the clay shrinks, the pieces of grog move closer together. When the pieces of grog come in contact with each other, the shrinkage stops. Adding too much grog to a body can make it very stiff and non-plastic.