Expert: Leisha Hiester - 2/4/2009

Question
I teach middle school art. We have some some plaster molds. We have tried pouring slip  made from bonedry scraps and water, thinned more than we use for our coil built pots and mixed with a stick blender. Should we be using something to help release the clay from the mold after it sets some? We are having difficulty removing the clay, either too wet and sticks to the mold and tears or to dry and the clay develops cracks where it has shrunk. We do not have money in our ever shrinking budget to buy commercially prepared slip.Thank you for any help you can offer us.
Joy

Answer
Joy,

Are the plaster molds old? Molds that are worn out are difficult to use period. If the molds are in good shape, that's a good start.

Commercial slip is tricky enough. What you're attempting is possible, but difficult. The gravity of slip is usually measured and deflocculents used to make adjustments. Deflocculents are also referred to as slip dope. Instead of using water to thin slip, you first measure the gravity & add slip dope accordingly. Having the proper deflocculent makes all the difference. If you purchase this product from a supplier it comes with instructions. Good luck.

Leisha