Tuesday, March 8, 2016

February 28th Hint of the Week

Making Molds without Plaster.
Copyright 2001, Cindi Anderson, www.bigceramicstore.com
This tip isn’t technically about using plaster. It’s about how to use molds
without plaster. What if you don’t want to use plaster, but you still want
press molds, or slump & hump molds. Never fear, as there are other options!
  • Bisque - You can make press molds out of clay & bisque them. These work quite nicely & clay doesn’t stick to them. Carve the inverse of your desired design into leather hard clay. For example, if you want raised lettering, carve the letters out of the press mold & the inverse will be raised. Remember to make your design about 10% larger than desired, to account for shrinkage.
  • Bisque also makes great slump & hump molds. These can be thrown, or handbuilt, or molded from a found object.
  • You can use found objects (mixing bowls, platters) directly by coating with vegetable oil, PAM, WD-40, etc. or by covering with plastic wrap or newspaper. Usually you will use these as slump molds, as the insides of your bowls & platters have the nice curvature you are looking for.
  • Wood - Wooden bowls can often be used directly without any coating. Wood is porous & often is oiled or has a slick finish so clay won’t usually stick. You can also dust the clay or wood with corn starch if you are afraid it will stick. Keep an eye out for wooden bowls at garage sales.
  • Canvas - You can also make a sling out of canvas & use that for your mold. For example, take a piece of canvas & put it over the top of a large round garbage can. Where the canvas overhangs the can, wrap tightly with string or wire. Place your slab on the canvas. You can get different curvatures depending on how tightly you pull the canvas. This same technique can be used with buckets for smaller slabs.
  • Here’s a great variation on the previous idea, which I just thought of! You can cut holes in the canvas where you want the feet to go. That way you can attach the feet while the clay is still wet, & not have to worry about getting it off the sling at exactly the right time, when it is hard enough to hold the shape but still soft enough to add the feet! Cool huh?
  • A similar approach to the above is to put the canvas over a plywood box. Staple the canvas to the outside of the box. Again, the curvatures can be modified by how tightly you pull the canvas. You can staple just two ends, or all four ends for different effects. If you want to make this more versatile, make a version where you can vary the amount of curvature. Attach screws or nails to the outside of the box.
  • Or, (here’s my laziness coming through again… I’d rather think of a better idea than go to the trouble of making a plywood box), how about using clothes baskets! They come in round or rectangular, & are inexpensive.
  • Newspaper - Another thing you might consider is making a form out of loosely crumpled & dampened newspapers. This allows a looser look. Shape the damp, crumpled newspaper into the form you like, & cover it with plastic. The newspaper will dry & this hump mold will likely be useable for a while. If it starts to come apart you can squirt the newspaper with water & re-shape.

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