Big Ceramic Store Blog

Monthly Archives: April 2015

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    This tip isn't technically about using plaster. It’s about how to use molds without plaster. But what if you don’t want to use plaster, buBt you still want press molds, or slump and hump molds? Never fear, as there are other options!

    1. Bisque

    You can make press molds out of clay and bisque them. These work quite nicely and clay doesn't stick to them. Carve the inverse of your desired design into leather hard clay. For example, if you want raised lettering, carve the letters out of the press mold and the inverse will be raised. Remember to make your design about 10% larger than desired, to account for shrinkage.

    Bisque also makes great slump and hump molds. These can be thrown, or handbuilt, or molded from a found object.

    You can use found objects (mixing bowls, platters) directly by coating with vegetable oil, PAM, WD-40, etc. or by covering with plastic wrap or newspaper. Usually, you will use these as slump molds, as the insides of your bowls and platters have the nice curvature you are looking for.

    2. Wood

    Wooden bowls can often be used directly without any coating. Wood is porous, so clay doesn't stick. Keep an eye out for wooden bowls at garage sales.

  • Sometimes it is difficult to catch a pot at the perfect leather-hard stage for trimming. But if you try trimming when the clay is too wet, the trimmings gum up your tools and get stuck to the piece. However, you can trim if you keep the pot well lubricated with water during trimming.

    Dip you hand in a bucket of water and spread it over the pot. Do this periodically, and the trimmings slide off easily.

    Try it! Just be careful of pushing too hard if you've trimmed a lot and used a lot of water, as your piece may have softened up and you may push it out of shape.

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  • There are many ways to get interesting patterns in your clay.

    Look around your house, your yard, and especially your kitchen, and you will start to see all kinds of things that can make good textures. Rocks, the bottom of your shoe, the wheel of a toy truck, a meat tenderizer, a piece of driftwood. The list is infinite, but for our more experience potters, here are a few of our favorite impressions.

    Complex Patterns

    1. Bisque rods. Make a bunch of coils of clay. For example, a good size is 1" diameter and 8" long. The main problem with bigger diameters is the time it takes for the clay to dry before firing. But you can set these aside and let them dry for a good long time. While the clay is still soft, carve or press patterns into it. For example, poke the end of a needle tool in to make holes. Or press the edge of a ruler in to make lines. Cover the whole surface with your pattern. After drying, bisque fire the pieces. Now you can use these rods to make patterns in wet clay. Simply roll your rod across the clay, pressing while you roll, and you can make long, continuous patterns.
    2. Take wood dowels and apply patterns to them with hot glue. When the glue dries, the dowels can be rolled across the clay to make similar patterns.
    3. Wrap string, twine or rope around a dowel in straight or criss cross patterns. Roll over the clay.
    4. Carved Linoleum. We got this idea from a potter who used to be a printmaker. Linoleum was used for flooring before we had the vinyl floors of today. Linoleum is a mixture of linseed oil and cork. When heated, it becomes soft so you can carve into it. Then it hardens when it dries. You can get linoleum at art supply stores. At the same time, you can buy a set of carving tools. Either draw or trace a pattern on the linoleum, then carve it out with the tools. You can use very intricate designs, such as a tree with many branches and leaves. The textures transfer very nicely to the clay.

  • For Amaco, Laguna and Spectrum glazes (other than Novas), when you purchase them in liquid form (pints, gallons, etc) they are are formulated for brushing. When you purchase them in dry form, they are formulated for dipping, pouring or spraying. Coyote glazes (and Spectrum Nova glazes) are formulated the same whether purchased in liquid or dry form.

    As a general rule of thumb, for 1 lb of dry glaze powder, use 11 ounces of water for dipping glaze, 8 ounces of water for spraying glaze, or 7 ounces of water for brushing glaze. Or, 25 lbs makes about 3 gallons. This is only a starting point.

    To use a dry glaze for brushing, a brushing medium, such as CMC or glaze medium may be added. CMC acts as a binder and allows the glaze to flow smoothly. If you purchase CMC or brushing medium in dry form, it is best to add those to your dry glaze before adding water. Or the liquid forms of CMC or brushing medium will mix more readily into glazes that are already mixed.

    To mix a dry glaze, first add bentonite to the dry glaze to keep it in suspension and increase the drying time. Not all glazes will need this. It depends on the composition. Bentonite is mixed at approximately 2 grams (.0044 pounds) per pound of dry glaze.

    Measure water into a clean plastic bucket. Mix the measured amount of glaze into the water as best as you can. Then pour the mixture through a sieve into a second bucket, pushing the clumps through the sieve with a rib or other tool. Repeat several times.

    Note: Glaze recipes sometimes specify a mesh to use, and that will affect the outcome of the glaze. Otherwise, for glazes, 80-100 mesh are most common (lower numbers are usually for mixing slips).

    Optionally, a hydrometer could be used to check the viscosity of the mixed glaze. The hydrometer reading should be approximately 900-1000 for dipping, 1500-1700 for spraying, and 2200-2500 for brushing.

    Let the glaze sit for 24 hours, remix, then use.

    Glaze should be stirred often, as contents can settle during use. If the glaze thickens over time, you can usually just add water.

    Some people find that if they use a power mixer they don't have to sieve their glaze. The sieving process accomplishes 2 things.

    1. Makes sure the glaze is well mixed.

    2. Gets rid of lumps.

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  • Here are a few handbuilding tips we've come across in our travels. Have a few you want to share yourself? Drop a comment!

    1. Having trouble with clay sticking to your molds, rolling pins, and canvas?

    • Use pantyhose to cover molds, rolling pins, etc.
    • Sprinkle the surfaces with cornstarch. It will burn off in the kiln.
    • Cover items with Saran Wrap or newspaper.
    • If you're using the slab roller a lot, the canvas can get wet and cause sticking. Use separate pieces of cloth (old sheets are great and you can get them at garage sales for 25 cents) or thick plastic instead of placing the clay right on the canvas.

    2. To keep tiles and other pieces of clay flat as they dry, sandwich them between pieces of drywall. You can stack many layers this way.

    3. To support your slabs while handbuilding, try cutting your templates out of roofing paper (tar paper) or cardboard. They will support the slabs so you can assemble them while they are still soft. Keep it attached until the clay hardens, then peel off.

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