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Fully Dry Your Green Pottery
When pottery is first made, it is loaded with water. All atmospheric water must be evaporated as much as possible before the pottery is ready to be put into the kiln. Otherwise, problems with the clay body are quite likely to occur. Be sure to dry your pots slowly and evenly until they are completely bone dry. The stage before bone dry is leather hard, this is when the moisture has nearly left the clay. It's important to be aware that ceramic work is at its most fragile during this time,... when it is drying out.
Remember: Glazes and clay bodies need to be matched for temperature maturation as closely as possible. In nearly all circumstances, low-fire clay bodies should be used with low-fire glazes. Mid-range or high-fire clay bodies will remain too porous or "punky". If you use the incorrect glaze for the clay, then it can have a big impact on the color you are trying to create.
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The second step is to bisque fire your pottery. Load the kiln carefully and be sure to set the kiln sitter before placing the upper kiln shelves. (Most electric kilns are equipped with these helpful devices.)
Since we are talking about bisque firing low-fire clay bodies, we can fire the clay slightly higher than the glaze. Usually, this means you will bisque fire to cone 04 (make sure you get the zero in there!), which will tighten the clay body just a bit more than a lower temperature will. We... have defined bisque firing as 'referring to a ware which has been fired once and has no chemically bonded water left in the clay'.
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Once the pottery has been bisqued, cooled, and removed from the kiln, you can decorate it. Glazing your pottery can be an adventure of discovery, especially when you are using new glazes or using familiar glazes over a new, different colored clay body. The possibilities with glazing are endless, and you can dip or paint on your glazes. You can also use effects such as marbling, transfers or underglaze painting.
Remember to use wax resist and coat the pot's bottom and up it's outer sides... a quarter of an inch before using underglazes and glazes. Wax resist is used so that the pot does not stick to the bottom of the kiln and risk cracking the pot and ruining the kiln shelves.
Raw glazes are not at all the same color they will be once fired, which can stretch your imagination as you work to envision what the finished piece might look like. If you have examples of the fired glazes, you may find it helpful to keep them near where you can use them as a reference as you glaze your new pots. It's important to note that raw firing is not as robust as glaze firing and if you are using it, it's better suited to decorative pieces, as it will not food safe. Raku firing is a type of raw glazing and can have the most beautiful effects.
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Glaze Fire Your Pottery
Stack your glazed pieces in the kiln after they are completely dry (usually just a few hours). Stack carefully; give pots a quarter inch clearance space on all sides and at the top.
The firing schedule for glazing is faster than for bisqueing. This is because the bisque firing has already transformed the clay into a ceramic material. Low-fire glaze firings are usually between cone 06 and 04, with cone 05 being very common. A typical firing schedule is:
- two hours with ramp at 150°F/hr
- three hours... with ramp at 400°F/hr
- ramp at 120°F until the desired temperature is reached.