The process of making a pot or bowl on the potter's wheel is a physical one. The object is brought to life through the potter's hands and fingers. Centering, lifting, shaping, forming, coiling, collaring, smoothing, cutting, joining, the process of making is described by "doing" words that are expressive of physical effort and touch. My favorite ceramic objects are usually ones where the potter has not turned the piece excessively with a metal tool, or smoothed away all evidence of having been made by a human hand.
|Throwing demonstration at the Otago Museum in 2015. Photo Rhonda Beck.|
Imagine how boring it would be to a visit to an art gallery if all the paintings in it had been airbrushed, if your favorite Monet, Rembrandt, Frans Hals, De Kooning, or Bonnard, had no visible brush strokes and their canvasses were flat and smooth!
One of the pleasures of handling hand made pottery is being able to pick up the item and feel weight, balance, and texture. This pleasure is denied to the viewers of blogs... so we will just have to rely on the eyes and some imagination.
I thought I would introduce you to a porcelain bowl that I glaze fired part way through February. The bowl was probably around 15 1/2 inches (393mm) when wet and slimmed down to about 12 3/4 inches (324mm) in diameter when fired. Porcelain shrinks a great deal when it is fired because it becomes glassy and vitrified. visualize of a pile of powder mysteriously turning into a puddle of liquid, and you will see what I mean. This makes porcelain strong, non absorbent, and translucent if thinly thrown, but the extreme shrinkage makes it hard for the potter to visualize the final size.
The bowl has a deep foot underneath it that I added when the bowl was leather hard and still a little pliable. There are a number of ways of adding a foot to a bowl, one is to leave the base very thick to start with and then to remove surplus clay with a loop tool, another would be to throw a little cylinder of clay and add that when the bowl and the cylinder are leather hard, but, when making a deep foot ring on a large bowl I prefer adding a coil of clay, centering it, then throwing the coil to its finished size. I sometimes cut out little half round openings in the foot with my cut off wire.
I used 4 glazes on the bowl, and I applied them by pouring. I hold the bowl in one hand, and pour glaze from a small saucepan full of glaze that is held in the other hand. I do this over an old metal Wok, which usually succeeds in catching most of the run off glaze!
The first to go on was BTM (black tenmoku)
This is a saturated iron glaze that gives a lustrous brown black when fired to a high enough temperature. I like to fire the top part of the firing slowly when using this glaze, and hold the kiln near the peak temperature for half an hour or so.
Over that went a good splash of a Janet deBoos clear glaze (number 144 from her first book) that I modified by adding rutile and copper carbonate. This gives a nice pale green glaze over a white clay, or a variable optical blue when over a dark glaze or clay.
Over that went AV1 which is a dolomite matt glaze that gives a smooth, slightly oily feeling glaze when used by itself on a pot. Over a saturated iron glaze it gives lacy patterns which vary a great deal depending on how thickly this glaze is applied.
Finally I poured on a splash of a saturated iron glaze that gives a lustrous red. This is based on a recipe that may go back to the Chinese Song Dynasty. I found it in a 1997 Ceramics Monthly article about a wonderful potter from Taiwan called Wang Chun Wen.
The bowl was fired to cone 10 in an electric kiln. The firing was done slowly near peak temperature to give time for the glazes to mature and intermingle nicely.
55 Nepheline Syenite
10 Ball Clay
8 Red iron oxide
DeBoos glaze 144 Cone 9 - 10 (modified)
40 Potash Feldspar
10 Ball Clay
5 Zinc Oxide
+ 3 rutile
+ 2 copper carbonate
AV1 cone 10 a high magnesia/alumina silky matt glaze probably best in reduction.
34.7 Potash Feldspar
Wen/Conrad translation of Chinese recipe. I modified this (the original called for 10% red iron oxide and 4% Edgar Plastic Kaolin, I added 9 % yellow ocher to supply some of the iron, and all of the clay to the recipe. I also adjusted the silica and feldspar amounts to take account of the change of clay.).
47 Potash feldspar
10 Bone Ash
9 Yellow Ocher
8 Red Iron Oxide
The original Wen/Conrad translation was as follows
10 Bone Ash
4 Edgar Plastic Kaolin
10 Iron Oxide