|Antique Ceramic here refers to all types of objects made from clay and fired in a kiln, and being at least 50 years old. Ceramic is among the oldest of materials used to make functional objects.
Fine antique ceramic pieces may be decorated with underglazing, overglazing, gilding, or a combination of all three. In general antique ceramic collectibles fall into three broad categories, earthenware, stoneware, and porcelain.
Collectors of ceramics and porcelains need to be able to distinguish between the different materials in which an antique porcelain piece is made. Pottery is much coarser in texture and includes porous earthenware and non-porous stoneware. The difference in these two types of
ceramics stem from the use of different materials, the temperature at which it is fired, and the proportion of vitreous fluid (glassy) ingredients in the body.
Earthenware and stoneware are both forms of pottery, which is fired at temperatures up to 2400 degrees and is opaque when held to the light. Porcelain, however, is fired at 2550 degrees or higher and is translucent. In general, porcelain is much higher in price than pottery because of its structure. Over the years, new processes and techniques have been developed which fall into other subgroups of these categories.
Many ceramic collectibles are covered with glaze. The glazes, which are made of silica and various other flux materials, metals or minerals used to promote fusion, determine the color, hardness and texture of the
ceramic. Glazing also keeps moisture from penetrating the body of the work.
There is a difference in the glaze process applied to antique ceramic earthenware and the glaze processes of stoneware and porcelain. On earthenware the glaze is physically on top of the surface, whereas the glazing on high-fired
ceramic pieces, such as stoneware and porcelain, is chemically bonded with the surface, making it much more durable and chip resistant.
Decoration may be applied to antique ceramic pieces at different times within the glazing and firing process. If the ceramic is underglazed, the decoration is applied after the initial firing, but before glazing and final firing. Common underglazing materials include cobalt oxide, which turns blue during firing.
If the antique ceramic piece is said to be overglazed, this means that decorative enamel paint and flux materials are added after glazing, then the piece is fired again, causing the paint to fuse to the glaze. Overglazed designs can usually be felt on the surface of the
If the ceramic piece has gilding, a thin covering of gold, this is added last in the process and requires that the piece fired at lower temperatures.
Collectors may often hear the term of "crazing" used to describe an antique ceramic piece. Crazing is a network of tiny cracks occuring in the glaze. Crazing is considered unattractive by many antique collectors, but does not necessarily indicate damage to the piece. It is the natural aging process caused by expansion and contraction as a result of changes in temperature and humidity. Ceramic is not generally easily affected by these changes, but is advisable that the collector take care in handling and placement of their
ceramic collectibles in order to avoid possible deterioration or breakage. (For more information, see our page on caring for your antique ceramic collectibles.)