This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
It is of the highest importance in selecting oxides, minerals, etc., for manufacturing different articles, for potters' use, to secure pure goods, especially in the purchase of the following: Lead, manganese, oxide of zinc, borax, whiting, oxide of iron, and oxide of cobalt. The different ingredients comprising any given color or glaze should be thoroughly mixed before being calcined, otherwise the mass will be of a streaky or variegated kind. Calcination requires care, especially in the manufacture of enamel colors. Over-firing, particularly of colors or enamels composed in part of lead, borax, antimony, or litharge, causes a dullness of shade, or film, that reduces their value for decorative purposes, where clearness and brilliancy are of the first importance.
To arrest the unsightly defect of "crazing," the following have been the most successful methods employed, in the order given:
Flux made of 10 parts tincal; 4 parts oxide of zinc; 1 part soda.
A calcination of 5 parts oxide of zinc; 1 part pearl ash.
Addition of raw oxide of zinc, 6 pounds to each hundredweight of glaze.
To glazed brick and tile makers, whose chief difficulty appears to be the production of a slip to suit the contraction of their clay, and adhere strongly to either a clay or a burnt brick or tile, the following method may be recommended:
Ball clay............ 10 parts
Cornwall stone...... 10 parts
China clay.......... 7 parts
Flint............... 6.5 parts
To be mixed and lawned one week before use.
Pottery or any soft or even hard stone substance can be cut without chipping by a disk of soft iron, the edge of which has been charged with emery, diamond, or other grinding powder, that can be obtained at any tool agency. The cutting has to be done with a liberal supply of water fed continually to the revolving disk and the substance to be cut.