Today’s Quick Tip addresses a question sent in by a Ceramic Arts Network reader. This reader wondered if we had any tips for judging the size of a hole on a piece of pottery that is designed to receive a cork, stopper, or clock movement. Well, it just so happens that New York potter Lili Krakowski created just the gadget to help ensure the right fit every time. Take it away, Lili! – Jennifer Poellot Harnetty, editor.
Throwing neck and gallery openings to a specific fired size is a frequent problem, but using corks as “measuring sticks” can make this task much easier. Corks are sold in graduated sizes, and are available from ceramic supply companies and local hardware stores. Purchase a complete assortment. This system has served me well for years. Wearing heavy work gloves, use a single-edge razor blade or mat knife and cut two V notches from top to bottom on each side of the cork (figure 1). The notches prevent the cork from creating suction when in use. Mark the size on the top of each cork with a waterproof marker. Add a screw eye to the top to facilitate storage and also to serve as a handle (figure 2).
To create your gauge, throw a large, bottomless ring approximately 4 inches high, and set aside so it can be leather hard at the same time as your “spouts.” Next, throw a series of straight-sided spouts 3–4 inches high and size them with the corks (figure 3). When sizing the opening, the cork should only be inserted halfway. Clean the inside of the spout well (figure 4). Set the spouts aside to set up to leather hard. I throw each spout on a bisque tile so I can keep the cork I used with it throughout the drying process.
When the spouts and ring are leather hard, attach the spouts to the outside of the ring, marking each spout with the ID of its cork. You can cut holes in the ring where the spouts are located, but it is not necessary. Dry the ring slowly to minimize warping, then bisque and glaze fire the ring. Because shrinkage rates vary depending on clay type and firing temperature, you’ll need a separate ring for each clay body and final firing temperature.
When making a gallery for a lid, use a smaller cork to size the actual opening of the piece and the bottom edge of a larger cork to size the diameter of the gallery (as shown in the diagram at the left).
Lili Krakowski is a professional potter residing in Constableville, New York.