Secondary clay

Description

Clay that has been deposited away from the site of the parent feldspathic rock. Secondary clays are often carried downstream by rivers producing a fine particle, highly weathered clay that is deposited along the banks or in estuaries. Secondary clays tend to be very plastic and, without the addition of other materials, may shrink severely when dried. However, in most cases, secondary clays have naturally combined with other other minerals, such as silica, iron oxides and calcium carbonate, that can minimize shrinkage. Additionally, any alkaline oxide impurity can act as a flux when the clay is heated and lower the sintering point of the clay. Iron oxide impurities may add red or yellow color to the clay.

See also clay ball clay, clay red clay, clay calcareous clay, clay siliceous clay, clay fire clay, clay stoneware clay, clay fusible clay, marl.

Synonyms and Related Terms

sedimentary clay; ball clay; arcillas secundarias (Esp.); secundaire klei (Ned.); barro secundrio (Port.)

Authority

• Henry Hodges, Henry Hodges, Artifacts: An Introduction to Early Materials and Technology, Ronald P. Frye, Kingston, Canada, 1988

• Robert Fournier, Robert Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Company, Radnor, PA, 1992

• The Dictionary of Art, Grove's Dictionaries Inc., New York, 1996 Comment: "Ceramic"