Ceramic is a generic term for a range of products that are made from inorganic, non-metallic materials, usually fired at high temperatures. It includes glass, earthenware, stoneware, porcelain and bone china. The word "ceramics" is from the Greek word "keramos" which means "Pottery".

Earthenware - Is pottery that has been fired at a temperature of around 1100 C. It is not vitrified. It is porous and needs to be glazed in order to be functional.

Stoneware - Is pottery that has been fired at a high enough temperature (1200 to 1300 C) to partially vitrify (melt together and fuse) the material and make it somewhat impervious to liquids. It is usually covered with colored glazes. If you look at the unglazed bottom ring of a stoneware mug you will notice that the body is cream colored as compared to the white body of a porcelain mug.

Porcelain - Is made with kaolin clay. Kaolin is a white clay that retains its white color when fired. It is fired at temperatures in excess of 1300 C and is more fully vitrified than stoneware. Porcelain ware was first made in China; hence it's commonly referred to as CHINA. It is usually covered with a clear glaze, which allows the white body to show. If you look closely at the surface it appears that the white body has a glass coating on top. The unglazed bottom of the mug will show a white body material.

Porcelanous Stoneware - Is stoneware that has a very white clay body. It is covered with a clear glaze or white glaze. It is more vitrified than regular stoneware but not as vitrified as true porcelain. Mugs made with porcelanous stoneware are usually considered to be porcelain mugs.

Bone China - Is a very translucent white china. One of its component ingredients is bone ash (or it's chemical equivalent) which gives bone china it's translucence and stark whiteness. Bone China is usually very thin and if held to a light source it is translucent.

While the definitions listed above are those most commonly used in our industry, for purposes of duty classification the US Customs defines the various types of ceramic items by the amount of absorption each type has. Below is a listing of the definitions from the Harmonized Tariff Schedule of the United States (2002).

(a) The terms "porcelain," "china" and "chinaware" embrace ceramic ware (other than stoneware), whether or not glazed or decorated, having a fired white body (unless artificially colored) which will not absorb more than 0.5 percent of its weight of water and is translucent in thicknesses of several millimeters. The term "stoneware" as used in this note, embraces ceramic ware which contains clay as an essential ingredient, is not commonly white, will absorb not more than 3 percent of its weight of water, and is naturally opaque (except in very thin pieces) even when absorption is less than 0.1 percent.

(b) The term "bone chinaware" embraces chinaware or porcelain the body of which contains 25 percent or more of calcined bone or tricalcium phosphate.

(c) The term "earthenware" embraces ceramic ware, whether or not glazed or decorated, having a fired body which contains clay as an essential ingredient, and will absorb more than 3 percent of its weight of water

(d) The water absorption of a ceramic body shall be determined by ASTM test method designated C373 (except that test specimens may have a minimum weight of 10 g, and may have one large surface glazed).

The Federal Trade Commission (FTC) is charged with preventing deception and unfairness in the marketplace. To this end, the FTC has published guidelines for what products can be legally claimed to be "Made in USA".

To learn more about this subject, simply click on the following link to go directly to the FTC's web site dealing with this topic. http://www.ftc.gov/bcp/edu/pubs/business/adv/bus03.shtm

A small void of glaze on a fired mug is typically known as a “pinhole”. Pinholes in ceramics are the result of volatile organic materials outgassing during the firing. There are always some small percentage of organic materials in the clay of the mug bodies. During the firing, these organic materials will oxidize and the resulting formation of CO and CO2 will be driven out of the body, through the glaze, and into the atmosphere. Occasionally, the outgassing will cause a bubble to form in the glaze. When this bubble expands enough, it will break and cause a small crater in the glaze. While the glaze is still in a viscous liquid state, it will usually flow back into the ‘crater’ and fill it, thereby smoothing out the glazed surface. Sometimes, the bubble will break just as the cooling process is starting and if the glaze starts to thicken during the cooling, it can become too viscous and stop flowing before the crater has been filled and healed over resulting in a small pinhole.

One way the occurrence of pinholes can be reduced is to fire the unglazed mugs to allow the mug to outgas completely, then applying the glaze to the mugs and re-firing them. This added firing increases costs considerably. Because of the added cost and time, this process is usually reserved for high-end dinnerware. Almost all of the ceramic mugs used in the decorating industry are single fire and the pinhole issue is controlled as much as possible through careful firing. This allows the best compromise between acceptable quality and price. While all reasonable efforts are made to control the formation of pinholes in ceramic mugs, it is virtually impossible to eliminate them completely. This is generally well known in the decorating industry and accepted as the norm.

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