What is Salt Glazed Pottery?

If you're an admirer of antiques and vintage finds, you've probably come across the term "salt glaze" in your perusal at shops and auctions. I'd seen examples of salt glazed pottery long before I'd heard the term. Typically, on heavy, old earthenware, a salt glaze is identifiable by its clear, shiny appearance. Its translucence and slight orange peel-like texture can be found on everything from antique beer and water bottles to serving bowls and platters. Antique sewer pipes were also often salt glazed. The reason we can find such a variety of examples of old salt glaze pottery is that it was the first glaze used on bisque earthenware to render it waterproof. According to Mandy Parslow at www.parslowpottery.com, salt glaze was first developed in Germany around the 15th century. Unglazed bisqueware was not completely waterproof as moisture could seep through, so the arrival of salt glaze was quite an important development in earthenware. The process of salt glazing is quite simple. Once the kiln reaches a very high temperature (1660-2200 degrees Fahrenheit), dampened common salt is added. Steam forms within the kiln during firing and the sodium from the salt reacts with the silica of the clay to create the glass-like coating known as sodium silicate. According to "Salt Glazed Stoneware" at www.antique-marks.com, color shades can also be used in the salt glaze process. As well as the completely clear salt glaze produced by just common salt (sodium chloride,) iron oxide can be added to create brown; cobalt oxide to create blue and manganese oxide to create purple. Vibrant blue is considered the hallmark of salt glaze ceramics and is very desirable in the antiques market. From Germany, the production of salt glaze spread throughout Europe and finally to colonial America in the 1600s. The rugged pottery dominated the ceramics market right up through the 1880s. Every household had a number of salt glaze pieces such as crocks for pickling (the acid didn't affect the tough salt glaze,) butter churns, water and beer storage, serving dishes and bowls for food preparation and many more everyday functions. Not every salt glaze was utilitarian however and the artistry of these clay and salt creations was not secondary to its usefulness. Almost parallel to the evolution of salt glaze pottery is the development of porcelain. Originating in China (which is why porcelain is commonly just known as China,) porcelain comes from a non-absorbent white clay and though often more delicate in heft and appearance than earthenware, it's technically even tougher. It's translucent to a point and also gives off a certain ring when tapped. By the late 19th century, the production of salt glaze was all but stopped except for in art pottery. There were two reasons for this. One was the rising popularity of less expensive glassware, particularly with the introduction of a certain jar created by Mr. Mason. The second reason for the overall end to salt glaze production is its harm to the environment and to the individual potters who created it. During the firing of salt glaze, the salt (sodium chloride) mixed with water vaporizes and forms hydrogen chloride which is at its lowest level still irritating to the eyes, nose and throats of individuals working with it. More extreme reactions in humans is permanent damage to internal mucous membranes necessary for survival. Hydrogen chloride or hydrochloric acid is also extremely bad for the environment because of its corrosive properties. Antique salt glazed pottery is collectible and there are certain hallmarks to look for when seeking higher valued pieces. First, look for that shiny, glass-like surface with a slight orange peel feel to it. Then look for pieces that are decorated. Hand-painted cobalt blue art on a pottery piece is highly desirable. Look for visible brush strokes in the blue decoration. The decorative elements should also appear underneath the glaze, not applied on top. A stamp or a maker's mark is also a good sign the piece has value. There are a myriad of guides available for researching just what manufacturer used what type of mark or imprint. You never know what you might uncover if you do the research. That $25 pottery jug you bought at a yard sale could be the work of a highly revered master artisan and be worth thousands!