Page:Architectural Review and American Builders' Journal, Volume 1, 1869.djvu/425

 1868.] Porcelain, Glass, and Pottery. 347 only the clay for the base of the porce- lain, but the fusible material or feld- spar. Those rocks containing but a small proportion of mica, yield a better clay (less fusible) than those in which this mineral preponderates. A mixture of feldspar and quartz, or the rock called by mineralogists pegmatite, produces, caerteris paribus, the best Kaolin. The writer of this article has exam- ined, Jn his professional capacity, both in the field and in the laboratory, many American Kaolins, not a few of which were fully equal to the best of the for- eign ; and has seen these clays tried by reputed skilled workmen, in the produc- tion of Porcelain, always with the same result, and that result a Failure. He is satisfied that the lack of that min- ute and delicate attention and care, so requisite in the preparation of the glaze, has been the cause of the repeated ill- success of American Porcelain. To amplify a previous paragraph, the Moors first i-e-es_tablished in Europe the manufacture of pottery as an art, after the knowledge of it had become in a measure lost, during the Dark Ages suc- ceeding the subversion of the Western Empire. Throughout Spain are found numerous evidences of the perfection to which they carried the production of the finer qualities of ornamental pottery, more especially in the manufacture of the beautiful tile known still as azueljo. From Spain, the art passed into Italy, one of whose styles was Majolica ware, (a corruption of Majorca,) and thence a knowledge of it was disseminated throughout Europe. But it soon lost its prestige and high position, the dis- cover}' of the composition of Porcelain causing that material to supersede the coarser and older earthenware proper,- or potteiy, and leaving for this latter no further demand, than for the commoner domestic articles. In the hands of Wedgewood, in England, the plastic art seemed destined to regain, in a measure, its pristine importance and splendor, in all its departments ; yet the majority of his wares also approximate, in physical properties, as well as chemical composi- tion, to porcelain rather than pottery. As the transition from glass to porce- lain was a gradual one, so from the latter to pottery there is no less an easy gra- dation, so much so, that both Wedge- wood and stone wares — intermediate steps from porcelain to earthenware — may indiscriminately be classified either with the former, or be described as pot- tery. In a strict technical sense, though not in an sesthetical one, they belong to the earthenware division of the Ceramic art ; for we may define this last as in- cluding all those varieties from which is absent any flux, and which, being fired at a temperature sufficiently low to pre- vent even a semi-fusion of its component parts, is never translucent, but always opaque, and possessed of an earthy frac- ture. Potters' ware, being destined for the most ordinary purposes of domestic life, must combine in its manufacture essen- tialities to meet the requirements of low prices, imperviousness to liquids, and durability under changes of temperature. The first is satisfied by the wide-spread and abundant occurrence of the ordinary clays, by the use of inexpensive methods of moulding, and by burning in kilns of cheap construction, which shall consume the possible minimum of fuel. This latter condition produces a material of a light, porous structure, which, to meet the second requirement, must be coated with a thin glaze, generally of a very fusible lead glass. The third condition is satisfied by mixing or tempering the clays, when, too fat or unctuous, with sand, or lean clays, to diminish contrac- tion. The porosity of unglazed earthenware is finely illustrated, and its properties utilized, in the ordinary water-coolers or cooling-jars of tropical America. A clay vessel — moulded in fanciful and, often- times, not ungraceful forms — baked without glaze, and filled with water, will soon be coated on its outer surface with