Sizing is a process of applying a thickening agent or mixture to cloth, paper, etc. The change brought about is distinctly physical. The object of sizing is to add weight, strength, and smoothness (luster) to the material. A considerable variety of substances are used in size mixtures, the more important of which are included in the following list:

(a) Substances possessing adhesive properties to strengthen the material and fix other ingredients. This class includes flours and starches of wheat, sago, rice, maize, and potatoes.

(b) Substances to render the material soft, pliable, and smooth. This class includes tallow, grease, oils, wax, glycerin, and soap.

(c) Substances to make the material heavier. This class includes French chalk and salts of barium and sodium.

(d) Substances to destroy or prevent the growth of germs that cause mildew. Zinc chloride is almost exclusively employed for this purpose.

(e) Deliquescent substances to attract moisture to the material, whereby it may retain its pliability, and to prevent powdery substances from being rubbed off. This class includes magnesium chloride, calcium chloride, glycerin, and common salt.