Medium Temperature Bodies

M325 - Buff Middle Stoneware			M332 - Middle Brown
M332G - Middle Brown Sculpture Body			MSculp - Heavily Grogged Buffstone (14% 20-48 grog, 14% silica sand)
M350 - Tan Middle Stoneware			M340 - Buff Middle Stoneware
M390 - Red Middle Stoneware			P300 - Porcelain
M370 - White Semi-Vitreous Stoneware			P380 - Porcelainous Stoneware

Most hobbyists and educational institutions work in medium temperature electric kiln firings. These kilns are relatively inexpensive and make it possible for almost anyone to produce extremely durable and hard stoneware pottery. This type of stoneware has the advantage of being quite reproducible also.

A huge range of glaze effects is possible in middle-fire. The middle temperature range has its own charm, but it is also possible to emulate terra cotta and majolica and even produce the earthy and speckled effects achieved in iron reduction bodies in high temperature (i.e. some of our middle fire bodies are available with granular manganese added to produce specks that melt and tend to come up through overlying glazes).

Generally Plainsman middle fire bodies are targeted to be 'visual' at cone 5 and optimally mature at cone 6. At the lower temperature the surface is generally variegated and 'warmer' in color, at the higher one it is usually more homogeneous and stony looking.

Working and Drying Characteristics

We have included information on this in each data sheet. In general you will find that our middle temperature stoneware materials share the same good workability qualities as our high fire materials. However, bodies made from refined materials are generally less plastic because more feldspar and other fluxes are needed, making less room available in the recipe for clay.

Firing

In the medium temperature range the vast majority of ware is fired in electric kilns. These do not have good air flow so you must allow time during the early stages for ware to expel the water and for the vapor to drift out of the kiln. Increasingly electronic kiln controllers are being used in middle temperature kilns and these provide the capability of programming a very slow ramp at the beginning. Additionally they make it possible for a precisely controlled soak at the end of the firing to assure pinhole and blister free glazes.

Glazing

Middle temperature provides some of the advantages of both high and low fire glazes. The heat available will melt most ceramic minerals and thus not nearly as much flux is needed as at low temperatures. However not as much silica and alumina can be used, this means higher expansion and more trouble with crazing. Although it is possible to make purely raw glazes (no frit) this is usually done with high amounts of nepheline syenite or soda feldspar, both of which contribute to crazing. It is often best to use some low expansion low melting boron frit as this will allow the use of additional kaolin to harden the dried layer and suspend the slurry.

Since much functional ware is fired at medium temperatures, it is important that your glazes fit your clay body, from a ware strength, aesthetics, safety, and functional point of view. A visual inspection is not enough. A simple boiling water:ice water cycle test of two minute duration per switch is suitable to bring out most crazing or shivering. If you need help to match a glaze and clay or strengthen your ware (doubling the strength is not unusual with a better fitted glaze) check the web page at http://www.ceramicsoftware.com/education/glaze.

We do not recommend that you have more than two or three base glazes (one is ideal). It is better (and cheaper) to understand how to adjust one glaze to vary its color, surface, expansion, character, etc. than to have twenty recipes that you cannot control. Check the web page at http://www.ceramicsoftware.com/education/glaze/cone6.htm for information on how to make and control your own base glaze.

Since most middle temperature ware is fired in electric kilns, we recommend that you monitor firings closely to make sure that they are in fact going to the temperature your controller is set to. Be aware that different zones in the kiln often fire to different temperatures. Since the glaze surface benefits greatly from soaking, you will find an electronic controller to be a tremendous benefit in producing the best ware possible.

Glaze Recipes

Visit the web page at http://digitalfire.com/education/glaze/cone6.htm for a good glossy and matte base glaze with lots of information on controlling the two to create any effect you want.

Plainsman Clays Ltd. 702 Wood Street, Medicine Hat, Alberta T1A 1E9 Canada

Phone: 403-527-8535 FAX: 403-527-7508