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Roger Keane |
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Choosing a clay body for tableware production |
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One
of the most important aspects of quality ceramic domestic
ware today is durability and strength. Before ware is
marketed it should be fully tested for practical functionality,
glaze fit, glaze durability and mark resistance, glaze
toxicity, body strength (modules of rupture - M.O.R),
apparent porosity, edge chip resistance, microwave and
dishwasher suitability as well as thermal shock resistance.
Whilst glaze toxicity should be lab tested, there are
many other tests which can be carried out by the potter
with a little ingenuity and a common sense approach.
For example plunging the ware into hot water then cold
several times in succession in an effort to accelerate
the onset of shelling or crazing; if it is prone to
craze it will. Using the ware in your own domestic environment
will reveal any weakness in manufacture or design. Pottery
books, magazines and encyclopedia provide valuable information
on suitable tests that can be carried out by the potter
in a kitchen. Ware which passes all these tests can
be expected to be durable and give a satisfactory period
of service. Durability of finished contemporary ware
begins with consideration of ;
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1. Appropriate selection, and preparation of raw materials; 2. Correct design, according to materials selected 3. The manufacturing processes through to the finished product. The appropriate selection and use of the raw materials can be accomplished by purchasing them from a knowledgeable and reliable supplier. When working with earthenware clays, where porosity is high, it is extremely important to achieve good glaze fit. For example, Keane’s white earthenware and terracotta clays have been formulated to fit a range of commercially available glazes. All are food safe and correct application and firing will produce a high quality finish. For stoneware and porcelain temperatures, recipes should be available from your supplier. These will provide a starting point for further development. The element of durability is largely dependent on design, shape, form and structural details of the ware; the correct design of functional ware according to the properties and nature of the ceramic material used. Earthenware, stoneware, mid-fire and porcelain each have their own different design criteria in regards to rims, feet and body thickness. Often we see earthenware which has been inappropriately copied from stoneware or porcelain and vice versa for stoneware and porcelain. The Italians have been successfully making and using earthenware vessels for centuries. Their master craftsmen show an understanding for making durable ware, by makings their rims and bodies much thicker than conventional stoneware. Also glazing all over and firing on stilts. Their foot rings are fine because they do not have to support a pyroplastic body in the firing. Dry footed earthenware reduces its durability and strength. The ancient Chinese have shown their mastery of stoneware and porcelain and whilst contemporary table ware may not follow their shapes and forms, their fastidious attention to rims and feet provides an excellent reference, which we can apply to today’s ware. Well made and designed contemporary stoneware and porcelain is more durable and possesses more strength than earthenware; however, each has its own important qualities and appropriate usage. For instance earthenware would not be considered suitable for hotel kitchenware, whereas colourful and well designed earthenware can be a sheer delight in the domestic situation. Contemporary earthenware stoneware, and porcelain domestic design is developing in a colourful and innovative direction, compared to that of early Australian pottery. Maintaining a high standard of durability and strength, as well as a unique modern style, will ensure the continued acceptance and popularity of hand crafted ceramic domestic ware for the future. Roger Keane - Keane Ceramics Technical archive |
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