Ceramic Design Studio

Vapor Glazed Pottery
Kosai 12 Kosai 13 Kosai 01 Kosai 02
Kosai 03 Kosai 04 Kosai 05 Kosai 06
Kosai 07 Kosai 08 Kosai 09 Kosai 10 Kosai 11
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Contemporary vapor glazing firing techniques often yield remarkable visual effects. Vibrant and exciting rainbow-like colors and designs are imprinted on ceramic ware by fuming certain chemicals onto the surfaces of glazes that have a high metallic content and onto which a layer of precious metals has been applied.

The product of this unique process is known as Kosai ware (Japanese term for hue of light). The emerging and stunning colors are likened to Newton’s rings, scientifically described as thin film colored interference fringes due to the reflection of light rays between a spherical and a flat glass surface. On a ceramic glazed and fumed surface, the effect is readily compared to that unique rainbow color pattern seen when water covers an oil spill on asphalt.

Fuming works well with many glazed surfaces. Although a mother of pearl effect can be produced on light or clear glazes, the more dramatic Newton’s rings are better seen on metallic glaze surfaces covered with gold, platinum or bronze. The multi-firing technique I use can involve as many as seven kiln firings.

    The first firing is called bisque (cone 04) and serves to “harden” the raw clay.
    The second firing matures the first glaze application which can range from 1800°F to 2400°F.
    The third firing matures a second glaze application at a lower temperature than the first.
    Sometimes an optional third glaze is applied with a fourth firing.
    The fifth firing serves to fuse the precious metals to the surface.
    The sixth firing constitutes the vapor glazing with selected chemicals (bismuth, barium, strontium, tin or iron). It is application of a thin layer of these metals that causes the interference of light and the separation of the colors of the light spectrum as they reflect off of the glaze surface.
    The seventh firing can be a smoke firing to darken surface cracks that may have developed.

As you can imagine, considerable time and skill is involved in making and successfully firing any given piece of Kosai ware, not to mention the expense of securing refined chemicals, precious metals (i.e., real gold), and glaze materials.

Kosai ware is durable, that is, the brilliance will not fade in time nor when periodically exposed to the sun. Kosai ware can be cleaned with water.

Do not store nor serve food in it. It is not oven, microwave, nor flame proof.