From the "good dishes" to those little "what nots," we've all got special artifacts made of clay and glass.  The American Institute of Conservation offers these guidelines for keeping them sparkling.  Many special objects are made of ceramics or glass. These materials cover a tremendous variety, including porcelain, earthenware, “crystal,” Depression glass, pottery, and art glass to name just a few. Jewelry, dolls, sculpture, tableware, tiles, kitchenware, and many other items can be made from ceramics and glass. Ceramics are made from different types of clays that are modified and colored by additives. The clay mixture, also called the body, is formed into shapes using a variety of techniques such as coiling, turning, and molding. The shaped objects are heated to drive off water and realign the crystalline structure of the clay. The clay is compacted, and sometimes melted, during firing, which results in shrinkage of the object. Ceramics are often classified by their body type. Earthenwares are porous and often coarse-bodied ceramics that have been fired at relatively low temperatures. Stonewares can also be coarse-bodied, but are fired at a high enough temperature that the stoneware body is impermeable to water. Porcelains are very fine-bodied ceramics that are fired at very high temperatures to create a vitrified, or glasslike, body. Ceramics are often decorated with colored slips and glass slurries and are then glazed for decorative purposes or, in the case of earthenwares, in order to provide water impermeability. Glazes are usually slurries of ground glassy materials, often mixed in water, that are coated over ceramic bodies and fired into a glass layer on the ceramic body. Colorants and other minerals modify the glaze to produce different colors and effects. By controlling the amount of oxygen in the kiln and the firing temperature, the potter can produce a variety of wares even from the same clay. Raku is a form of Japanese ceramic that has been fired in an oxygen-low reducing fire in the kiln. Glass objects are made from a mixture of ground silica (sand) and other mineral modifying agents (usually metallic salts) that are melted together to create a molten glass. The molten glass is formed by a variety of methods, including molding and blowing. The shape is then allowed to cool and harden. If a glass object is not allowed to cool slowly and properly by a process called annealing, it will crack or shatter from uneven internal stresses.