Throwing a good plate can be difficult. Once you've mastered the basics of compression and learned to add a good rim, you still have to cut the plate off the wheel or the bat without gouging the bottom. Canvas bats to the rescue.
In my years as a ceramic artist, I have never come across a tip or tool that changed how I felt about making a particular object as much as the canvas bat altered my feelings about plates. It solves most of the inherent issues of making plates, allowing you to cut the object off the bat with relative ease and not lose any clay or gouge the bottom.
Here is how it works: Canvas is cut into circles of varying diameters. The easiest way to do this is to take your bat, trace it onto the canvas, and then cut. I have also seen this done using tarpaper, so give that a try if you have some available. The canvas should have a good weight; canvas weights range from 4–12 ounces per square yard, somewhere around 8 ounces works well for this process. If the canvas is too thin it does not stick well and can bunch or slip as you are working. I affix the canvas to the wheel head or bat with a little bit of slurry; the amount you need is dependent on the surface it is attaching to, so start with a small handful. Once the slurry is spread across the wheelhead (1), the canvas is then laid on top (2) and pressure is applied to help it adhere and remove air bubbles. You can apply pressure while the wheel is spinning (3). At this point a small amount of water can be added, which releases the tension in the canvas and helps it stick. However, adding too much water or slurry can cause the canvas to slip during centering or throwing. Once the canvas is secured, begin throwing as you normally would (4). When the object is complete, remove the pot from the surface it was thrown on by cutting between it and the canvas (5). It may help to use a rib first to lift the edge of the canvas, creating a path for the wire tool. Allow the piece to dry as you normally would. When the object is ready, flip the piece over and pull the canvas from your plate (6). This moment is rather glorious—the plate is level and no clay was lost in the process. The texture left by the canvas can be removed during the trimming process. I use the canvas bat primarily when making plates, it can be applied to almost any form.
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