In the matter of glazes, it requires a great deal of skill and long practice to tell one from another. All are transparent, with the exception of tin or stanniferous enamel. Felspathic glaze is that most readily recognized; but in the case of the others--the alkaline, plumbiferous, and boracic--they are very often only to be distinguished by their different effects upon the colors used in decoration. CHAPTER III. COMPOSITION OF WARES AND GLAZES. Hard and Soft Pottery and Porcelain.--COMPOSITION OF PORCELAIN: Kaolin--Its Derivation and Ingredients--Petuntse--How prepared in China.--The European Process.--Differences between Chinese and European Porcelains.--Chemical Analysis.--English Porcelain and its Peculiarities: Its Average Composition.--How English Clay is prepared.--French Artificial Porcelain.--Parian.--COMMON EARTHEN-WARE.: Table of Ingredients of different kinds.--General Table.--GLAZES: Classes.--Brongniart’s Classification.--Difference between Enamel and Glaze.--Silicious Glaze.--History.--Use of Oxides.--Egyptian Processes.--Metallic Lustre.--Stanniferous Enamel: Its History. The division of pottery and porcelain into two great classes, hard and soft, is based upon the difference of their composition, their hardness of surface, and their power of resisting the action of fire. The simplest test is scratching with a knife or other instrument. Hard porcelain and pottery resist the metal, while the soft is marked. The former will also stand a temperature in the kiln at which the latter would crumble or fuse.