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A small area surrounding our home in western PA is the only place I have ever seen ceramic blocks used for building, instead of concrete blocks. The foundation of our 100-year-old home is made with ceramic blocks, as are a tool shed and a huge garage that was once a sulky barn for a nearby harness-racing track (long gone.) Many old commercial buildings in our area are made from the ceramic blocks, as well as a few silos.
The blocks have been salt glazed. Instead of applying a liquid mixture of minerals that will turn to a glassy glaze in a kiln, salt is thrown into the kiln once it reaches the desired temperature. The salt immediately vaporizes coating everything in the kiln with a thin glaze. In the process, dangerous chlorine gas is emitted ---and that is why the kiln must be outdoors. Today kilns used for salt glazing pottery are usually fueled with natural gas, but 100 years ago they may have been fueled by wood fires.
The resulting blocks come in various shades, ranging from pale yellow through tan to a deep reddish brown and have a texture that somewhat resembles that of an orange peel.
The process is very unpredictable. Hotter areas, where flames reach the pottery directly, usually result in glossier surfaces and richer hues. The timing of the introduction of salt into the kiln, the moisture content of the salt, how much salt glaze is on the inside surface of the kiln from past firings, how close a block is to flames in the kiln, the exact mineral content of the clay ---all make a difference in the outcome.
I like the warm and varied shades of the blocks ---so much more interesting than plain gray concrete ---but after 100 years the mortar holding them together is deteriorating in some areas. With time, shifting has caused a few of the blocks to crack. It is advised not to leave salt-glazed pottery outside in freezing temperatures. Obviously, our ceramic blocks have seen 100 winters of freezing weather.
One reason why this might have been a common way to make building blocks in our local area, is that salt-glazed ceramics were first created in Germany in the 1500s. No one knows if the first instance was an intentional or accidental occurrence. German immigrants to America used the technique to make crocks for storing food and liquids. The soil in the town where I live has high clay content and this area was settled by German immigrants who probably brought knowledge of the technique with them.
Even with shifting populations, about 80 percent of the population in our town has German roots. When we moved here 22 years ago, we didn't know that, yet between my husband and I, we have 5 grandparents of German descent.
In the mid 20th century, salt glazing was adopted and perfected by Japanese and American potters to create beautiful works of art.
Click HERE to see examples of salt-glazed pottery by Tom Davidson of Youngstown, OH. By clicking on the images to enlarge them, one can see the 'orange peel' texture on some of the individual ceramic pieces.
(text & photo, ©2009 C.J. Peiffer)