A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . require the consistence of the thickeningto be varied ; such as the nature of themordant, its density, and its acidity. Astrong acid mordant cannot be easilythickened with starch; but it may be byroasted starch, vulgarly called Britishgum, and by gum arable or mordants which seem sufficientlyinspissated with starch, liquefy in thecourse of a few days; and being apt torun in the printing-on make blotted France, this evil is readily obviated,b
A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . require the consistence of the thickeningto be varied ; such as the nature of themordant, its density, and its acidity. Astrong acid mordant cannot be easilythickened with starch; but it may be byroasted starch, vulgarly called Britishgum, and by gum arable or mordants which seem sufficientlyinspissated with starch, liquefy in thecourse of a few days; and being apt torun in the printing-on make blotted France, this evil is readily obviated,by adding one ounce of spirits of wine tohalf a gallon of color. The very same mordant, when inspis-sated to different degrees, produces dif-ferent tints in the dye-copper; thus, thesame mordant, thickened with starch, fur-nishes a darker shade than when thick-ened with gum. Yet there are circum-stances in which the latter is preferred,because it communicates more transpa-rency to the dyes, and because, in spiteof the washing, more or less of the starch. always sticks to the mordant. Gum has the inconvenience, however, of drying too speedily,and forming a hard crusrt on the cloth, which does not easily allow the necessary capillaryattraction to take place, and the tints obtained are thin and meagre. The substances gen-erally employed in thickening are:— 1. Wheat flour. 2. starch. 3. Torrefied wheat starch, or British gum. 4. Torrefied potato farina. 5. (lum substitutes or soluble gums. 6. Gum Senegal. 7. Gum tragacantb. 8. Salcp. 9. Pipe-clay or china-clay mixed withgum Senegal. 10. Sulphate of lead. 11. Molasses. 12. Dextrine. 13. Albumen of eggs. 14. Glue. CALICO PEINTING. 247 Those most used are the first seven. The rest are only adapted for special styles orcolors. The artificial gums produced by roasting starch or farina are very largely in action of heat on starch causes a modification in it. According to the degree of heatand its durati
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