Ceramic Chemistry

PREFACE. Modern Ceramics may be said to date from Brogniart 1770-1847. The predominance of the French chemists in the science of pottery during the early and middle parts of last century caused the word Ceramic to be transplanted into English and German. Seger and his colleagues then caused potters to turn their eyes to Berlin for a generation but there are not wanting signs that many of Seger s conclusions are being seriously questioned by the present school of ceramists. New vitality has sprung from the foundation of the American and English Ceramic Societies and from the adoption of the science as a subject for degrees in many American Universities. That Ceramics is suitable for University study both theoretical and practical there can be no doubt. It is the natural means of transition from Geology to Chemistry, Mathematics, Physics, and Engineering. No other subject unites those five sciences so intimately. If this book should promote the secondary and higher study of the subject in England, the writers aim will be accomplished. He wishes to express his indebtedness to the Transactions of the English and American Ceramic Societies. 292432 H. H. S. CERAMIC CHEMISTRY. v. CONTENTS. Page Preface ... . y Introduction Chapter. - - - . I. Geological Origins II. Clay III. Clay Analysis vii. - - - 1 - 12 - 17 IV. Raw Materials - 30 V. Bodies 37 VI. Glazes 46 VII. Enamels 52 VIII. The Production of Colour 59 IX. Firing of the Ware - X. Loss in Manufacture - - - 71 XI. Industrial Disease - - - 75 XII. Testing of Finished Ware - - - 79 XIII. Classification of Pottery XIV. Research - . ... XV. Bibliography in English Index of Authors - 65 84 - 82 - - 85 Index of Subjects 89 87 CERAMIC CHEMISTRY. vii. INTRODUCTION. Ceramic chemistry is concerned chiefly with the reactions of silicates. It is complicated by the difference in conduct between body and glaze. In the latter, if properly matured, the chemical reaction between the constituents has proceeded to a finish, and the melt consists of a homogeneous mixture or solid solution of silicates and, it majj be, borates and phosphates, and any eutectics that may be formed. With the body, on the other hand, it is different. The firing is only conducted to incipient vitrification, if as high as that. The chemical reactions are not allowed to proceed to a finish. The chemistry of pottery is therefore, as far as the body is concerned, one of incomplete reactions. Consequently, the nature and condition of the raw materials are of im- are irrelevant portance in the body, while in the glaze they as long as the same ultimate composition is preserved. CERAMIC CHAPTER I. GEOLOGICAL ORIGINS. The composition of the earths crust has been estimated by several observers, the latest being F. W. Clarke 1901, who based his calculations on 830 analyses of typical samples of the primary rocks, and found an average of Silica 59. 71 per cent. Alumina 15.41 ,, Ferric oxide 2 . 63 Ferrous oxide 3 .52 ,, Lime 4.90 Magnesia 4 . 36 ,, Potassium oxide 2 . 80 Sodium oxide 3 . 55 ,, Water of combination 1 .52 Titania 0.60 Phosphoric anhydride 0.22 ,, 99.22 per cent. Which leaves less than 1 per cent, for all other combinations of elements. Clarkes figures have the molecular formula Na2O 0.173 K2O 0.090 A1O 045 SiO2 3.0 aO 0.264 I F o 8 Oo49 Ti 2 022 I MgO 0.327 P2 5 0.005 FeO 0.146 J The melting point of such a mixture would be about 1,200 C. As the temperature of the earth, according to the figure adopted by the British Association, increases 1 C. for every 117ft. in depth, it follows that we have at least 25 miles of solid earth beneath us. Owing, however, to the pressure of the superincumbent strata, the melting point of the rocks is probably raised appreciably, but the depth given indicates a minimum limit. The specific gravity of the primary rocks of the earths crust is 2...