Monday, February 6, 2017

February 5th Hint of the Week



Tips On Plates & Platters


 - Pottery Magic http://www.pottery-magic.com/

Making plates can be tricky, and the larger the plate the more likely you will encounter problems. Here are some remedies:
  • Make sure the clay is thick enough. Thinner plates are more likely to warp. Thickness should be even. Clay should be very uniform, work the clay well.
  • When rolling slabs, make sure you roll it out evenly in all directions, otherwise you could compress one side more than another and or have thinner places on one end or another.
    * When throwing, use soft clay but not too much water or the rim will get too floppy.
    * When you carry your wet clay slabs to a different place to form, make sure you don’t stretch it. Put it on a board, or roll it lightly into a sausage, then unroll directly on the mold that you will use.
  • Plates must be dried very slowly and evenly. Uneven drying can set up stresses that don't show themselves until the final glaze firing.
    * It can help to control drying so the center dries faster than the rim. To do this, cut a round hole in the plastic about 3-4 inches in diameter over the center of the plate.
    * Some people use water based wax to coat the rims during drying, to prevent them from drying too quickly.
  • For large platters, you probably need two foot rings, one around the outside and a smaller one left in the center. Otherwise the center of the plate may sag during firing.
    * When you place a platter on it’s rim, place it on soft foam to protect the rim and keep it from getting stressed.
    * Trimming large platters can cause slumping of the bottom during the trimming process. You can put layers of foam rubber or carpet pad into the center area before inverting * *  * * *Place a board onto foam rubber or rim then invert the whole thing to turn it over. This “holds up” the center area and prevents it from sagging. It is not necessary to fill the whole center of the plate. If you fill the center only (i.e. a 6” circular piece of foam rubber), it will keep it from sagging.
    * Another thing to use in a similar way is socks or larger fabric sacks filled with rice. The rice is malleable so you can push it around until you get the right shape.
    * Or still another item to use is a sponge.
    * Sharp tools make it much easier to trim without causing deformation. (Remember, clay has memory and even if you smooth out any deformations, they will come back during firing.)
  • Many people find firing goes much better when they notch the plates' foot rings. Warping, cracking, s-cracks, were all eliminated. The notches provided a way for air trapped under the foot to escape. If the gas can’t escape from bottom it may cause the center of the plate or platter to “bow” up. Just make small, U-shaped notches at the bottom of your foot ring.
    * Instead of, or in addition to these notches, drill small holes in the foot ring. This also allows the gasses and heat to escape, and also allows for a wire to be used for hanging. This is especially nice for plates that are too large to fit into standard upper kitchen cabinets. Some people use a single hole, others two close together, others 3 spaced evenly around the platter
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  • For plates and other items with large bases, make a clay “cookie” at the same time as your piece. This is a sheet of clay (the same type of clay), which you sit your piece during drying and firing. The cookie and the plate will shrink at the same rate. This seems to keep the piece from “hanging up” on the kiln shelf during shrinkage, expansion and contraction. For extra assurance, put a wash of alumna hydrate on the feet and the cookie.
  • Another method is to cover the shelves with grog. The folks who fire the kilns will put the grog on the shelf under the plate, just leave them a note.

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