Q. What do I do if my clay is too hard for me?
A. Clay lasts forever. The best way to soften clay is to make 1/2"-1" holes in the clay block, but do not go all the way to the bottom - a common broomstick works fine. Pour water into the holes, tie plastic bag tightly and let soak. The clay will absorb the internal water and soften to your needs, usually within 24 hours. Another way to soften clay is to wrap it in a wet cotton towel and cover it with plastic. This method takes a little longer, but may be eaiser in the long run.
Q. What if my clay is too soft for my taste?
A. The easiest way to firm clay is to open the bag and expose the clay to the air for as long as it takes to get to the right water density for you. Another way to firm very wet or "tired" clay is to spread it out on clean wood, canvas or plaster. Watch carefully, re-wedge & bag when at the right water content for you.
Q. What should I do with my clay scraps?
A. Many people reclaim their leftover clay. We usually recommend letting the scraps dry out completely and then placing them in a large container of water. The clay will slowly slake down. Drain off the extra water and spread out on clean wood, canvas or plaster to dry to the proper water density. Re-wedge & bag in heavy plastic. If large amounts are to be reclaimed, we recommend a pug mill. Porcelains are the hardest to reclaim because of fine clay loss during throwing and the extreme density of grolleg kaolin, which settles and hardens at the bottom. Add a little fresh grolleg to the mix when reworking porcelain or ball clay with others.
Q. Why are there so many kinds of clay?
A. Every clay body has a unique personality and language that it speaks. People are all different and respond to different clays in unique ways. Also, some clays are purposely formulated for special uses, such as raku, sculpture, lowfire, etc. Please ask us if you have any doubt as to which clays to choose for your personal needs.
Q. Do clay and glaze materials ever change?
A. Yes, and the main answer is in nature itself. Prepared clay bodies are composed of various clays mined in several locations throughout the world. Few clay and glaze ingredients are mined especially for the pottery industry. In fact, potters use less than 3% of the total raw clays and glaze chemicals mined. Mines are frequently required to change locations due to the materials running out or changing too drastically in composition. Fire clays, for instance, are mostly used in steel manufacturing and are not subject to the stringent quality controls needed for clay making. Kaolins are used in carpet backings, paper coatings, make-ups and are even additives in some foods. So basically, we are subject to trying to make the best of products that are not mined for us. The skill is in knowing how best to react and change when necessary.
Q. Why don't all glazes work with every clay?
A. A glaze must fit just right over the clay body. Too tight and crazing or shivering results, too loose and your glaze could crawl. Every clay body shrinks at a different percentage, as do glazes. Glaze is also affected by the ingredients in the clay bodies themselves. High iron bodies will almost always interfere with lighter glazes, giving off-colors or deepening darker colors. Combine this with the fact that materials sometimes change and it leaves you with a sense of wonder.
Q. Why do I sometimes get a hard settling in my throwing water bucket?
A. Some clays will have elements in them that are heavier and will tend to settle to the bottom. A simple solution is to add just a little common Epsom Salts into your throwing water. This will keep everything in better suspension and make clean-up easier.
Q. Will my reduction glazes work in oxidation?
A. Probably. However, some glazes will have a much different look, as will the clay body. Melt tests should be made on all glazes to give you a starting point. Minor adjustments might have to be made in the flux content.
Q. What is the best temperature to bisque clay at?
A. All clays are different. We usually recommend a bisque of 04, rather than 06. This is a hotter bisque and seems to release more gas from the clay, plus you get a stronger bisque for handling. Most glazes adhere fine. Fire slower in the medium range of 1000-1500°. Proper bisquing will eliminate many so called glazing problems such as crazing, bubbling and pinholing. Cleaning bisque by rinsing in water before glazing will also help remove any dust particles.
Q. Sometimes I get annoying little bubbles in my glaze, how do I fix it?
A. There are several reasons and several solutions. First try a slow 04 bisque to release more gases. Next try wetting the bisque piece before glazing to give smoother absorption. A slower firing could also solve the problem, along with a slower cool. Sometimes a fast firing will cause the glazes to boil and a fast cool will not allow glazes to smooth out. Using a Downdraft KilnVent system will also help the majority of glaze problems, plus give you a better, healthier work area and a longer lasting kiln.
Q. Is low-fire work food-safe?
A. To a limited extent which is dependent on clay & glaze fit. The glaze must fit snugly yet not allow any crazing. Crazing allows areas for bacteria to harbor. If latent crazing develops, it is no longer food safe. Over the long run we do not consider low-fire work food safe. We suggest you inquire about which glazes fit our lowfire bodies properly. Raku should not be considered food-safe because of glaze crazing and clay porosity.
Q. What is Majolica ware?
A. Majolica is a type of pottery that was traditionally done on a lowfire red clay. It is glazed with a tin-bearing white gloss glaze with fritted color painted directly on top of the unfired white glaze. The color being applied on top of the glaze sinks down into the glaze when fired and looks much softer than if an underglaze was used.
There are several new glaze stroke type glazes that are especially designed to make this pottery easy and fun to do. Amaco's GDC line has good color on top of LG 11 and Spectrum's DEC (Decorating Engobe Colors) which will go to cone 6. We are looking forward to working with both lines.
Q. What is a frit?
A. Frits are any part of a glaze recipe that has been melted and then reground. They generally are considered melters or catalysts in most glaze formula. Frits are made from chemicals that are soluble, like borax, to make them less likely to upset a glaze batch's fluidity. Substances like lead, antimony, barium and zinc are fritted to make them less injurious and or volatile. Ceramic stains are also frits since they are melted and reground carbonates and oxides. Frits are usually more reliable and predictable in some glazes.
Q. What is a general firing schedule for an electric kiln?
A. That kind of depends on what type of ware you are firing, what size kiln you are using and how full the kiln is. Bisque and glaze firings are different. Thrown pottery will need to fire faster than handbuilt or thick sculptural pieces. Yet, thrown pottery will need to fire much more slowly than poured greenware. The more clay mass in a kiln, the slower you should fire in order to achieve proper heat work and not strain your kiln. Don't forget clay mass also includes shelves and posts. A typical firing schedule for a medium sized kiln loaded with thrown pieces for a bisque should last around 10 to 12 hours with a glaze firing lasting around 8 to 10 hours. Nesting pots inside each other adds more clay mass and longer firing time.
If you are firing a switched kiln, without a downdraft vent, a good bisque schedule to begin with would be: Start with all switches on low and all peep holes open with the lid propped slightly for four hours. Then turn all switches to medium and close the lid and all peeps except the top peep hole. The top peep must remain open during the entire firing to provide necessary ventilation and room for heat expansion of air. Stay on medium for another 4 hours. Then turn all switches to high and let your kiln sitter shut off the kiln. The last thing you do is close the top peep hole to keep the heat in. Simply put, this is a 4-4-high schedule which should run from 10-12 hours.
If you are firing a switched kiln, without a downdraft vent, a good glaze schedule to begin with would be: Start with all switches on low and all peep holes open with the lid propped slightly for one half hour. Close the lid and all peeps except the top one. Leave the kiln on low for another two and one half hours. Then turn all switches to medium for three hours. Turn all switches to high and let your kiln sitter shut off the kiln. Close the top peep when the kiln shuts off to keep the heat in. Simply put, this is a 3-3-high schedule which should run from 8-10 hours. Adjust as needed.
Q. I like to Raku, but I don't like to make glazes? Is there an easy solution?
A. Basically, any lowfire glaze can be used for raku. Some of the glazes that still have fritted lead in them are very good candidates. If you do a long or heavy post reduction, you will probably get a color mutation, so test them first. Remember, a big part of the fun of raku is surprise.
Q. I have a glaze formula that calls for feldspar? Which one should I use?
A. If a glaze does not specify a particular spar, usually any potash feldspar may be used. There are several mines that produce potash feldspar. We sell G-200. Most of the time you may substitute it for Custer spar. Although there are some differences, most glazes are not that sensitive to the change. You should not substitute Nepheline Syenite with G-200 because it is much more active. If a glaze calls for soda spar, definitely use Kona F-4 or NC 4 soda spar.
Q. Are the fumes harmful from my electric kiln?
A. Yes. If you share working or living air space with a firing kiln, we think your health would be protected with a downdraft kiln vent. Some of the fumes emitted from an electric kiln are carbon, carbon monoxide and dioxide, sulfur dioxide and trioxide and fluorine. Some of the chemicals in glazes can emit lead, copper, chromium, cadmium, zinc, boric acid, barium and even feldspars sometimes volatize into unfriendly fumes.
Q. Why do some clay makers say there is only one point of vitrification for each body - say, cone 5?
A. Probably because they want you to buy their matching glazes. Firing a kiln is an art not a science, even with a digital firing you can not count on duplicating a firing. My cone 5 may not be your cone 5. Kilns can have a 1 to 11/2 cone difference from top to bottom, just from the hot air rise alone. Due to the different ways a kiln can be loaded and fired you can have a tremendous difference in clay working temperature (the actual "felt" temperature of the clay and glaze itself), even in the same kiln load. A heavily loaded kiln with lots of clay mass will fire just as fast as a lightly loaded kiln. The difference being that the very full kiln load will actually feel a little cooler to the clay and glazes due to more clay weight being heated. The lightly loaded kiln may feel slightly hotter to the clay for the same reason. Clay mass also includes shelves and posts.
We believe that you need a little leeway of usable cone ranges just to accommodate firing fluctuations. If you have any questions, please call.
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