“Salt Glazing” was developed in 13th century Germany—probably by accident. Historians speculate that these early potters collected salty driftwood or the scrap wood from brining barrels for use in their kilns. And a rather interesting result occurred: the pottery developed a thick, translucent and textured glaze which proved highly-durable—especially for jugs, crocks and other utilityware. In time, potters figured-out the “science” of this glazing technique and were able to duplicate and control the process. Eventually, ceramicists would add pans of salt water to the later stages of the firing process. This mixture would vaporize, releasing the sodium into the air which would surround the pottery being fired. This sodium would react with the silica and iron impurities in the clay, creating the special, textured finish of sodium silicate (which sometimes resembled the skin of an orange peel). The more salt used (or the higher the silica or iron content in the clay), the more textured the final glaze would be. Salt glaze coloring is fairly limited: mostly browns, some blues, and purple. Coloration is achieved by painting various chemical washes onto the pottery piece before firing it. As the sodium interacts with the chemicals in the clay (and the painted-on washes), a different, specific color results.
Salt glazing began in Germany and spread throughout Europe, England, and (eventually) the United States and Australia. At one time, most of the world’s commercial pottery production (especially utilityware like bowls, jugs, and sewer pipes) utilized the salt glaze technique. Of course, strictly decorative objects utilized other aesthetically-appropriate glaze techniques. In the post-War Twentieth Century, some studio (and commercial) art potters dabbled in salt glazing—sometimes to achieve a “twist” on modern aesthetics or as a “tip of the hat” to earlier ceramics technique. The two salt glazed vases pictured above are such examples. Made in the 1960’s, they are decorated with sgraffito incising, then glazed in the restricted color palette of salt glazed pottery.
Alas, all good things eventually come to an end and so did salt glazing. It seems that the release of so much sodium chloride into the atmosphere was highly polluting. Most developed countries now regulate the technique in large-scale operations though small studio potters sometimes revive the technique.