The process known as “raku” was first developed in Japan in the 16th century. I use relatively low-fire clay and I mix my own glazes from raw materials. After forming the clay and decorating it, it is bisque-fired in an electric kiln at about 900 degrees C. I then glaze the pieces and do a raku-fire in my Clay-Dog Raku kiln. I chose to buy this small kiln so I can lift the chamber by myself. Once fired, raku ware is not functional for food, drink or holding liquid due to its porous nature. Because of this, I’ve chosen to use the raku process to make work that can be used safely in different ways: e.g. salt and pepper shakers, mirror frames and soap dishes.
I use three different kinds of clay when making stoneware, two with iron in the clay body and one without (white stoneware). This high-fire clay was first fired in China around 1400 BC, and the ware is dense, opaque and non-porous. I decorate on the raw clay (greenware) and also once the clay has been bisque-fired, before glazing. I mix my own glazes from raw materials and after glazing I fire the work in an electric kiln (oxidation firing), reaching about 1230 degree C. All stoneware pieces are food- and liquid-safe, dishwasher safe and can be used in a microwave as well as a regular oven.
Porcelain is similar to stoneware but it becomes vitreous (glass-like) when fired. It consists of kaolin (china clay) feldspar and silica, all in small particles. When fired to a very high temperature these materials fuse and combine the refractory nature of clay with the vitreous quality of glass. Porcelain is thought to have been first discovered in northern China during the Tang dynasty (618-907) after which this white clay was found in the Korean peninsula, where the process was developed and refined. After forming the porcelain work and decorating it while it’s still fairly wet, I bisque-fire it in an electric kiln. I then decorate again, glaze the work with my own glazes and fire it in a gas kiln in a reduction (reduced oxygen) atmosphere to about 1300 degrees C. All porcelain work I produce is food- and liquid-safe as well as dishwasher-safe. It can be microwaved and used in a conventional oven, although it should be placed in a cold oven and warmed slowly.
Firing with wood is the oldest and most widespread method of producing ceramic ware, and was only supplanted by gas and electricity in the 20th century.Firing ceramic work in a kiln using wood as fuel can take several hours or many days, depending on the size of the kiln and the desired temperature to be attained.
The kiln is loaded by a group of experienced potters and students, using “wads” to stilt the pots and ceramic sculptures. This wadding will prevent the bottoms of the work from fusing to the kilnshelves, and will allow the flame to flow under the pot as well.
The kiln is then “bricked up” and sealed before lighting the kiln. During the fire, as the wood combusts it produces "flyash" and some volatile salts and minerals, which ultimately fuse with the silica on the surface of the ceramic pieces in the kiln, forming a glaze.
The placement of each piece in the kiln will determine the effects of the fire on the appearance of the pot, as the course of the fire leaves patterns and textures as clues to what happened inside the kiln.
The kiln is allowed to cool for several days after the end of the fire, the bricks are removed from the door opening and the ware is unloaded.
Before the next fire can be loaded, the inside of the kiln and all the shelves and kiln furniture must be "cleaned"--scraped and kiln-washed.
I buy most of my clay and materials at Northeast Ceramic Supply in Troy, NY. However, I live in the Hudson Valley and clay can readily be found in the earth here. A few years ago a group of potters heard about a deposit of Albany Slip Clay, and we went to search for it in a patch of ground in North Albany. We never found the deposit but we had fun, met some interesting folks, and got very muddy!
When my children were young they played in our pond, and realized the bottom was muddy with silt. I told them that they could find clay on the bank, and that if they wanted me to, I would fire the clay in my kiln. They soon found some earthenware clay, dried it in the sun till it was moldable, and made some clay faces from it. After firing, I used some of them, wrought-iron hooks and a slab of oak to make a hanging framework for fireplace tools.