The area to be tiled is carefully measured, and a design is created that complements the space. Joining slabs of moist clay, the clay base of the entire area to be tiled is laid out on a flat surface. If the area to be tiled wraps around corners, the clay slab can similarly be wrapped around vertical supports. Then additional clay is added to the base slab to sculpt the design. After the clay has become firm, the tiles are cut apart in a pattern that complements the design. Additional (false) grout lines may also be carved into the clay surface to enhance the design. The tiles must be dried slowly to prevent warping or cracking. The resulting tile installation will be unique to the intended space.
Hand-Made Flat Tiles
Moist clay is cut and pieced into a large flat shape, and then passed through a slab-roller that compresses and flattens the clay into the correct thickness. The surface is smoothed with a sponge, and the slab of clay is left to firm up. Tiles are hand-cut from the slab and the edges are smoothed and rounded with the fingers. Designs can be pressed into the tiles at this stage. The tiles are then allowed to dry slowly with frequent turning.
Hand-Made Bas-Relief Tiles
Using moist clay, a master tile is made by building up the relief design. The completed tile is placed on a non-porous surface and a mold is built around it. Plaster is poured around the tile and allowed to harden. The sides of the mold are removed and the master tile is removed and discarded. The resulting plaster mold is a “negative” of the tile. The plaster mold is allowed to dry completely; this can take as long as a week or more. When completely dry, the mold is filled with moist clay. This clay is pounded into the mold with a mallet. Excess clay is scraped from the back of the mold, and the back of the tile is smoothed. Over the course of an hour or so, the dry plaster absorbs water from the clay tile, causing it to shrink slightly. The mold is then inverted and the tile removed by tapping on the mold. The first few tiles are often used to make additional, duplicate molds. Molded tiles are dried slowly, sometimes with weights to reduce warping. C
When the clay tiles are completely dry, they are loaded into the electric kiln and fired. Although we sometimes refer to the maximum temperature to which the clay was heated, the accepted measure of firing is to a particular “cone”. Pyrometric cones (cone-shaped pieces of clay-like material) are formulated to bend after receiving a certain amount of “heat-work”, a combination of time and temperature. At Shubunkin Pottery, bisque firing is done at cone 04 (i.e., when an 04 cone bends the firing is stopped). The bisque firing burns out organic materials that can mar the final product, and makes the ware strong enough to withstand glazing.
Bisqued tiles can be decorated with underglazes (a type of colored clay that can be painted or trailed onto the surface of the tile) or with stains (colored oxides mixed with water). These tiles are covered with a clear glaze before final firing. Tiles can be made from either low-fire or stoneware clay bodies. Low-fire manufactured bisque tiles can also be used for decoration and glazing.
Tiles can be covered with a colored glaze that can be translucent or opaque, glossy or matte, and smooth or variegated. Stoneware tiles can also be left unglazed if desired, because after firing they will be vitrified and non-porous. (Low-fire tiles are too porous to be left unglazed). Glazes are formulated to melt and mature at particular cones, so low-fire glazes are used on low-fire clays, and stoneware glazes on stoneware clays.
Low-fire tiles are fired again to cone 04. Stoneware tiles are fired to cone 6. The firing takes from 12-14 hours, with an additional 12-16 hours of cooling before the tiles can be removed from the kiln.