How to Wedge and Test Clay to Make Ceramics
Professional potters who work on a moderately large scale go through a great deal of natural clay on a daily basis. The only way for this to be cost effective is to buy clay wholesale in economy sizes. This means they might buy several tons of clay at a time and store what is not being used outside under a tarp or in a shed. Over just a few short hours this clay can begin to dry out, but only the clay on the outside of the pile. The clay on the interior will stay moist longer. As a result potters often have to add a little moisture to their clay and thoroughly work the moisture in while trying to get any air bubbles or inconsistencies out. This is called “wedging” the clay because when you are finished you end up with an angular or conical shaped wedge of clay. Here is a guide on how to correctly wedge clay and test it to make sure it is ready to be used.
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Instructions
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Wedging and Testing Clay
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Place a lump of clay weighing several pounds on your work table. A piece about the size of a football should be adequate and is most easily worked.
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Crack open the clay, breaking it into several pieces to see how dry it is and get an idea of how much you will have to work the clay.
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Rub a little water over your hands and dribble some over the driest portions of the clay. You will have to use your own judgment on how much water should be used, but if you use too much you can always just let it dry out again before starting over.
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Crush all the lumps of clay back together and flatten them like a pancake.
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Roll the pancake up and fold it in half. There should be one or two angular edges of the clay. Take the clay in both hands, press a point against your work table, and press the clay downward firmly while rolling the top of the clay forward with your wrists.
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Pick the clay back up, press another point or edge against the table, and crush the clay downward again while rolling forward. Repeat this at least a dozen times. When finished you should have a conical shaped lump of clay. This is a wedge.
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Test the wedge by taking your length of cheese wire and pulling it through the wedge a few times. You should end up with three or four pieces of the wedge.
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Take each piece of clay in your hands and stretch it out, fold each piece slowly in half. As you fold the pieces you may begin to notice breaks and pockets appear in the surface of the clay. These are indications that large pockets of air are still in the clay, you will need to wedge the clay again. If you do not see any large empty spots or breaks on the insides of the clay then it is ready to be worked.
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Tips & Warnings
Some people prefer to affix a length of cheese wire running from a work table to the wall behind it. This way you can swipe the clay through the cheese wire, cutting the clay cleanly without having to put it down. This helps speed the testing process and maintain your rhythm in wedging the clay.
Clay that has not been wedged at all before being worked may have large air bubbles trapped inside. If a vessel or clay form is fired at high temperature like this it runs the risk of cracking and exploding violently as the air inside expands.
Resources
- Photo Credit pottery.about.com
