Friday, August 2, 2013

July Hints of the Week


 This interesting information from
  1. 1 cup takes about 1 pound of clay. 1 pint of glaze will glaze 12 cups
  2. 1 mug will take about 1 ½ pounds of clay. 1 pint of glaze will glaze 8 cups
  3. 1 bowl will take about 2 pounds of clay. 1 pint of glaze will glaze 8 bowls

These are some more tips from the Big Ceramic Store (copyright 2003, Cindi Anderson,
    1. To keep a piece from sagging while coil building or hand building, you are "supposed" to only build so far, then stop and let it firm up before you continue. But if you are impatient like me, a great solution is Duct Tape! Wrap it all around the piece so it sticks to itself (it won't stick to the clay.) This keeps the form from bulging so you can continue working.
    2. I am always looking for materials to make molds from. A unique method I saw recently was to use hard foam insulation board from the hardware store (the stuff that comes in 4'x8' sheets, usually 1" thick, and is often pink). You can use a utility knife to cut out shapes to use as slump molds. I am going to use this method to make some square plates.
    3. Another method works great for making plates, trays, etc. Find a block of wood (square or rectangular.) Cut a piece of clay larger than the wood. Put the clay on a large piece of upholstery foam. Take your block of wood and press down in the center of the clay. The sides will come up and make nice rims. This looks really great if you impress the rim with stamps before pressing in the center.
    4. By the way, if you don't have any upholstery foam laying around, get some! It is great for cushioning work while you clean and trim bottoms, so you don't damage the rims. You can often get free scraps from upholsterers.
    5. If you like to stamp, look for interesting textured buttons at fabric stores and flea markets. You can add handles by hot gluing thread spools onto the back, or pieces of thick irrigation tubing cut about 1" long.
    6. Another great idea I saw is to tape a small level onto a fettling knife. This way you can be sure you are making straight, level cuts.


Waterproofing and Sealing Ceramics (Tip #18 Big Ceramic Store)

.… Your best means of achieving a waterproof piece is to fire your clay body to the right temperature. But there are cases where you cannot make your ware completely waterproof.

For example, Raku firing does not achieve high enough temperatures to make the clay waterproof. Low fire clay also is not waterproof. Both will leak over time, if you leave water in them. This will probably happen even if you use glaze, because it is very difficult to get a perfect clay/glaze fit which will expand and contract together and not craze. (I have a mug that is a cone 10 stoneware fired at cone 6; it is fine with cold water, but when I put hot water in it the bottom becomes damp. What is happening is that when heated, the glaze probably expands and exposes tiny cracks, the hot water seeps through, and then through the clay. This will weaken the clay over time, and this piece definitely should not go through the dishwasher or in the microwave!)

The most common things I have heard potters say they use for waterproofing are:

  • Tung Oil (available in hardware or woodworking stores
  • Thompson's Water Seal (available in hardware stores, used for sealing wood and concrete)
  • Acrylic Floor Polish (i.e. Futura.) (available in the grocery store.)
Note that you should test any of these solutions because their waterproofing ability varies. And they will not work on air-dry/oven baked clays to make them durable and waterproof. Remember that kiln fired clay has changed into a glass-like form, and air-dry/oven clay has not. Also, you cannot use any of these for dinnerware. Just for vases, flowerpots, etc. And some people use them over glazes just to get a nice subtle shine, or on the bottom of pots to make them less likely to scratch furniture.

Another reason potters want sealers is to protect painted work. For example, people that use acrylic paints on bisque and want to protect the paint. We [Big Ceramic Store] do sell Duncan spray and brush-on sealers in flat and gloss, and Amaco All-Purpose Sealer which will protect the paint from chipping and smudging, and give it a shine if you wish. They are good for decorative pieces. But these are not waterproof. So if you want your piece to be waterproof, try one of the above products. But since those items work by penetrating the clay, and they probably won’t penetrate through the acrylic paint, I would put it on the inside of the piece, then protect the painted outside with an acrylic spray sealer like the Duncan products (or similar items available in the hardware store.) So for example, if you want to waterproof a flowerpot, put the tung oil, Thompson’s water seal, or acrylic floor polish on the inside of the pot. Paint and seal the outside.


Why is it called Throwing?

"This information is created by Lakeside Pottery, Ceramic School and Studio in Stamford, CT".

Origin of "To throw": Old Engilish - twist, to turn, to propel. Some potters describe their work at the potters wheel as turning. The Old English word thrawan from which to throw comes, means to twist or turn. Going back even farther, the Indo-European root *ter- means to rub, rub by twisting, twist, turn. The German word drehen, a direct relative of to throw, means turn and is used in German for throwing. Because the activity of forming pots on the wheel has not changed since Old English times, the word throw has retained its original meaning in the language of pottery but has developed a completely different meaning in everyday usage. Those who say they throw pots are using the historically correct term. Those who say they turn pots are using more current language. Both are saying the same thing.


How to Re-Glaze a Piece copyright 2000, Cindi Anderson,

First, note that this process is never predictable. In most cases you can make a new piece in less time than you can spend re-glazing it, with much more predictable results. But sometimes there is that piece you can't part with and really want to re-glaze. Here are some things you can try to increase your success rate. The goal, of course, is to get the new glaze to stick to the old glaze.
  • Spray the piece with spray starch, let dry, then reglaze.
  • Spray the piece with sticky hairspray (usually the cheapest you can find), dry, reglaze.
  • Heat the piece first, with a heat gun or in the oven or kiln.
  • Brush white (Elmer's) glue on, let dry, reglaze.
  • Microwave the piece for 30 seconds. (Some potters say this makes a huge difference, and the piece doesn't need to actually get or stay hot)
  • Add some suspension agent to the glaze (CMC gum or Bentonite.)
  • Add some detergent / shampoo to the glaze (baby shampoo is good because it doesn't foam)
  • To improve your odds further, wash the pot first with ammonia or detergent, wearing rubber gloves, and don't touch it. The oils from your fingers can prevent glaze from sticking.
  • And... Don't use too much of anything. If you get the coating too thick, you may prevent adhesion instead of encouraging it.

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