This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Clay Worsted. A variety of flat-twilled worsted woven with a twill similar to that of serge, the diagonal lines lying flat on the surface and barely perceptible. On account of the warp and weft being slackly twisted the cloth does not take a gloss as in the case of the ordinary hard-twisted worsteds. The name is derived from an English manufacturer, and it is from England that the best qualities are obtained.