Minnesota Clay Co. USA Technical Info - Ceramics Tips
Leave at least 1/2" between all pieces when loading your kiln. Remember that the piece will expand during the firing cycle before it contracts and shrinks.
When glazing a thin piece, glaze the inside, making sure you don’t over apply, as the thin walls will absorb a lot of glaze, then wait for it to dry thoroughly before glazing the outside. Otherwise the clay may be saturated and glaze won’t absorb and stick to the outside. Some people wait overnight.
To avoid pitting and pinholes in your glaze, be sure that your greenware is free of dust before applying glaze. A damp sponge will help to do the job.
Some glazes do flow more than others during firing, but it is impossible as a beginner to know which ones do and don't. You will have to rely on the knowledge of your teacher. Though a common rule of thumb is: the thicker and more varied the application the greater the tendency to run.
Practice makes perfect when learning brush strokes. Experiment a bit of applying different pressure to your brush tip to learn the effects different pressures have. When using your brush the more pressure you exert, the fatter the lines will be and the more colour you will lay down.
When loading your brush you should remember that you do not load a dry brush. When using glazes or underglazes, always dampen the bristles first before loading.
Be sure your hands are clean while working on greenware. Any kind of hand cream may cause stains or hard spots on fired ware.
Having quality ceramic brushes can make the difference between getting the result you want and frustrating creative failure. The paintings on your ceramics are what makes them stand out and gives them life. You should find out about the different kind of brushes available and how to care and preserve your brushes - especially those that you enjoy using the most.
You can find animal tails in fishing and hunting stores, sold as inexpensive lures. Use these to make handmade brushes. Chicken and bird feathers can make interesting brushes as well.
As with any tool, the better quality you buy, the better and easier the job becomes. The same applies to brushes. The higher priced brushes are worth their cost.
Wet your brush with water before applying water-based ceramic glazes or underglazes. If you are using metallics, translucent stains, lustres or your mother-or-pearls, wet your brush with the medium used to clean your brush. Always blott the excess out on a paper towel.
Feather stroking is a painting technique of using thinned paint about the consistency of milk with a flat brush. Short strokes are taken across a paper towel to split brush hairs for colour application. The brush is then dipped into two different colours and applied to the piece, gives great effects with swirls etc.
To build depth with a brush stroke, you can double-load your brush with two different colours. This is usually done by loading your brush with the lightest colour and tipping in a darker colour. Then stroke on the colour. The action of the brush will inter-mix colours. You should not try to get too many strokes out of one brush load however. Clean your brush and start again about every 2-3 strokes.
Brushes may be washed in soap and water as long as they are rinsed clean before use with a particular media.
If brushes do not come as clean as you want when cleaning in water, you can run them under the faucet. You may also wash brushes in mild detergent as long as you wash out the soap when done.
Old toothbrushes can be used for decorating ceramics. The bristles are stiff and can be used as a splatter brush. Also useful for joining when handbuilding.
Make sure you have a good layer of kiln wash on the shelf. This is to facilitate the removal of glaze drips. Do not apply kiln wash to the sides of the kiln, or underside of the kiln shelves. The wash is likely to flake off and land on your glazed pieces.
Never apply kiln wash to the sidewalls, lid or bottom of shelves, as it may fall off during firing and ruin your glazed ware.
There are two main stages in firing a clay object. The first stage, known as bisque or biscuit firing, converts clay into a permanent, porous material with the handling properties necessary for glaze application. The second stage, known as glaze firing, melts the glaze onto the pot.
For a bisque fire in particular, you need to drive off the water that is left in the pot. If you fire too fast, the steam will cause the piece to explode. (This is true even if the piece is very dry, because there is still moisture inside the clay molecules.) So it is important to fire bisque slowly. If your pieces are not completely dry, you may want to candle them first. Candling is done on a manual kiln by turning the bottom switch on low and holding it there for several hours (6-10). With an electronic kiln, you would program the kiln to remain at around 150 degrees F for this time.
Make sure your pieces are dry before loading them into the kiln. Pieces that are still wet will feel cool when placed on your cheek. Wet ware can blow up in the kiln, as the water inside the clay expands.
If you are having trouble getting your kiln to reach temperature, or the firing is taking extra long, the first thing to check is the power. If your kiln is too far from the breaker box, you may be getting voltage drops. Or if it is a hot, summer day when everyone is running their air conditioning, the voltage on your line is probably low. Speak to your electricty supplier about the best times to fire for optimum efficiency.
If you have a vent, you don’t have to worry about colors bleeding from one piece onto another. If you don’t fire with a vent this can be a problem, so you might want to segregate colors while loading
Peep holes in your kiln are used for observing the firing process so that you can see when the cone bends and when it is time to turn the kiln off if you do not have an automatic shut off. Peep holes have a secondary function in that they draw oxygen into the kiln, preventing reduction, and carry off smoke and water vapour.
Never ignite a gas kiln without opening the door a short way first. Accumulated gas can ignite and explode. Opening the door allows igniting gas to escape. If there is any question always referr to your owner's manual.
If the floor of your kiln has some rough spots caused from chipping off glaze drippings you can patch it with a special cement. You may also want to place an extra shelf in the bottom for protection.
The first few firings of a new kiln should not be glazed pieces. It may take a couple of firings to get all the moisture and vapors out of the kiln from the manufacturing process.
Some people wonder if it is ok to fire a kiln during very cold weather. It is, but Skutt in particular recommends warming the Electronic Controller (if you have one) to at least 40 degrees F with a space heater or hair dryer. Your kiln will have to work a little longer to get to temperature.
If you have a mold line that is difficult to remove from a piece of greenware, dampen the piece slightly. It will come off easier and lessen the chance of breakage.
If you are filling a crack in greenware with slip, be sure to work the slip into the cracks as deeply as possible to form a solid bond. You may find using a stiff brush will help, using a back and forth movement of the bristles.
To effectively use greenware mender, it is best to dampen both sides of a break with water and then apply a liberal amount of the mender to both sides of the break. It will form a bond in a few seconds.
Clay bodies are usually suited to certain types of work. A smooth clay which works very well on the potter’s wheel may have cracking problems when we try to handbuild with it. Large sculptures are usually built with very stiff coarse clay which would be unuseable for most other purposes. The temperature to which we’ll be firing our work and the fired color and texture we desire will also dictate what kind of clay body we choose to work with.
When you begin working with ceramics it becomes quickly evident that clay is at the center of everything. Not only the quality of your clay bodies but how you store your clay, how you prepare your clay for throwing and the different kinds of clay available for different ceramics projects.
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