Monday, October 21, 2013

October 20th Hint of the Week

Clay, Water & Drying

Clay & Water: When too much water is put on wet clay it can weaken the clay causing splits or collapse of the clay. This is can be true when attaching pieces such as handles, knobs or other decorations, water may work, but it is best to use 'slip' to glue pieces together. Slip is simply clay that has enough water so it is a thick liquid. You don’t need to have big buckets of slip but just a small container. It is advisable to use slip from the same clay that you are working with, or at least one with very similar shrinkage rates. You can make slip by mixing either powdered clay or wet clay with water or even magic water. Some potters also use vinegar. Beginners tend to overwork clay, so it is best to have a clear project in mind so you know exactly what to do at each stage and when to stop playing with it and wetting it. Try to avoid making pieces that are overly delicate and/or have a lot of fragile appendages and also not so wet, all of which will come with practice.

Drying: Clays shrink when they dry. Most of the time simply leaving an uncovered piece out to dry invites disaster, because some parts dry first, and then cracks emerge to relieve stress when the remaining parts dry and try to shrink at different rates. It is important for drying to occur evenly over the whole piece. In the summer pieces dry fairly rapidly and in the winter our heaters blow in some areas and accelerate drying too. It is important to have uniform thickness throughout your piece, but at least try to avoid very thick sections. The best way to dry is to put green ware one a rack with plastic to enclose the entire rack. However not everyone has room to have one of these drying or wet cabinets. Usually putting a plastic bag over the piece is sufficient. Some folks will even put a single layer of newspaper or light rag on the clay first and then the plastic over it. Newspaper or cloth helps absorb some of the moisture that condenses on the inside of the plastic. Many potters set their green ware on a board, called a ware board, so it can more easily be moved around in its fragile state. Plaster ware boards made from drywall are most popular as the plaster absorbs moisture. Make sure all the bare plaster, on the edges of the board, are taped, as chunks of plaster in your clay will ruin your piece. Some folks also put a piece of newspaper on their ware board before they set their piece on it. However, covering your piece with the plastic will slow drying down and letting it dry and shrink more evenly. After several days some potter’s will turn their bowls, mugs or other pieces upside down as the bottoms stay wetter longer. This exposes more of the wetter clay on the bottom (now on top) and lets some of the moisture wick down to dryer areas resulting in a more even drying and hopefully fewer cracks.

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