Ceramics

Ceramic is from the Greek word "keramos" meaning potter's clay; it refers to clay products made permanent by the application of heat. In addition to artistic endeavors, ceramics have many applications in industry where it is used for engine parts, electronics, medical equipment, and many other areas. When discussing art, this term is often used interchangeably with pottery. Ceramic artists, today, are sometimes referred to as "potters".

Clay

A naturally occurring inorganic substance composed of very small "plate-like" particles. These particles, when mixed with water as a lubricant, can slide past each other with relative ease. Known as "plasticity" or "workability", this gives clay its unique characteristic. Clay with finer particles is said to be more plastic than coarser clays but there is also more shrinkage during the drying and firing process. The various classifications of clay are determined by size, color, chemical make-up and purity.

Glaze

A glaze is a mixture of various materials and colorants, which are ground into a fine powder, mixed with water, and applied to ceramic pieces. This mixture, when exposed to high temperature during firing, will melt and vitrify, thereby forming a glass-like surface that is fused onto the ceramic piece. Glazes can be applied to dried unfired ceramics (greenware), or to ceramics that have been already been fired. Some complex pieces involve various cycles of glazing and firing to produce the artist's intended effect. Glazes are usually referred to by the temperature, or cone, at which they melt. For example a cone 10 glaze is a high-fire glaze. High-fire glazes tend to be more durable, but have less color, whereas low-fire glazes are more colorful but are less durable, and intermediate glazes provide a good compromise. When purchasing ceramic pieces, it is important to consider the type of glaze in terms of food safety, durability, and fit with the underlying clay body.

Firing

Firing is the general term for the process of exposing ceramic pieces to high heat in order to convert them into durable finished pieces. During firing, the clay and/or glaze go through a transformation whereby it is fused together into a solid piece. Unfired clay will dissolve in water, but the clay becomes impervious to water after firing. Although some fired pieces may still absorb water, this will have not an adverse effect on them. An experienced potter can achieve a wide variety of results by carefully controlling such firing factors as the rate at which pieces are heated and cooled, the presence of other materials in the kiln, and the amount of air (oxygen) that is present in the kiln. Often, pieces are fired several times at various temperatures levels in order to achieve the potter's desired results. Higher fired clays such as stoneware and porcelain tend to be less absorbent and more durable.

Bisque Firing

This term generally refers to the first (initial) firing if "shelf dried" clay. Also, pottery that has been fired but not yet glazed. The porous nature of earthenware means that it readily absorbs water, while other clays are almost non-porous even without glazing. The temperature of bisque firing is usually at least 1000°C, although higher temperatures are common. The firing of the earthenware that results in the biscuit article causes permanent chemical and physical changes to occur. These result in a much harder and more resilient article which can still be porous, and this can ease the application of glazes.

This term may also be seen as bisc, biscuit, bisqueware, bisquefired, biscuit. Bisque refers to both a preparation firing process and the pottery piece that has undergone the firing. The firing is to a temperature that brings about a physical and chemical change to clay. Atomically attached molecules of water are driven off the individual clay particles and they are fused together transforming them into one piece. This intermediate step in glazed ceramics gives bisque ware the ability to absorb water of the glaze solution causing the glaze materials to adhere to the piece while it maintains its shape. Considered to be in the "low-fire" range, some pieces are never fired above this and are therefore usually less durable.

Raku Firing

Raku is a Japanese inspired method of firing that creates unpredictable smoke patterns and spectacular metallic and crackle effects in the glazes. The term "raku" describes the piece as well as the firing process used to create it. After initially firing the piece in an outdoor kiln, it is glazed and fired a second time. When the temperature of the piece reaches between 1600 and 1800 degrees and the glaze has melted, the piece is very hot when placed in combustible organic materials (leaves, sawdust and pine needles) in a metal container and covered. The pit is covered, and the resulting fire and smoke add a wide variety of finishes to the piece. The process is quick, exciting, and predictable only within a certain range of possibilities. The result is a wide range of colors on the surface of the piece. The uniqueness or "one-of-a-kind" aspect of a raku piece is impossible to reproduce. No two pieces are alike. This, along with its shortcomings for functional use, is the reason raku is popular primarily for decorative purposes. This is called post reduction - during which the oxygen is burned out of the glaze taking the colorants back to a metal producing the metallic lusters seen in raku.

Saggar Firing

Saggar Firing was first used by the Chinese to keep wood ash off of their glazed pottery when firing with a wood burning kiln. Most saggar-fired pieces are fired in a gas kiln with combustible materials to color its surface. The saggar is sealed with a wad of thick kiln wash or high refractory clay. The results of each firing are different, and like raku, there are no two pieces of saggar pottery alike due to the fact that the potter does not have total control over the patterns that are created inside it. Potters use a wide variety of materials in a saggar firing. A little iodized salt, copper carbonate, copper sulfate, manganese, or red iron oxide may be added to a sawdust mix for added flashing. There are a lot of possibilities. Firing may include organic items such as dried manure, Epsom salts, various fruit or vegetable peels, nuts, pits, old cat or dog food, and different types of sawdust.

Ceramic Terms & Definitions

http://pottery.netfirms.com/assignments/assign/terms/glossary.htm http://www.columbus.k12.nc.us/echsart/CERAMICS%20DEFINITIONS.pdf