Starch cannot be considered as a pigment any more than flour. And while rye flour years ago was used in fillers and to a certain extent in roughstuff, the practice has been abandoned long since. It is well known that starch is a vegetable principle contained in many plants, and especially abundant in the various grains such as wheat, rye, rice, corn, oats, etc., in seeds such as beans, acorns, peas, etc., and in tuberous roots as arrow roots and more especially in potatoes. But the starch of commerce, such as we have to deal with, is mainly from corn or wheat and from potatoes. It is a white opaque powder, and its specific gravity is very low - 1.5. It is insoluble in alcohol, ether or cold water, but when united with boiling water and permitted to cool, the mixture forms a soft transparent paste. It can be made soluble by heating to the boiling point with glacial acetic acid or glycerine. By treating starch with dilute acids at 212 degrees F. it changes into that soluble substance we know as dextrine. When tested under a powerful microscope the various kinds of commercial starch may be distinguished from one another by the form of its grain or granules.
Potato starch grains resemble an oyster shell in form; wheat starch grains are mostly round or nearly round, while corn starch grains have a mark in the center similar to a cross or the letter Y. When starch is mixed with cold water it does not form a dough or become sticky like flour, but sets rather hard and is stirred with difficulty, especially when too much starch is used, twelve pounds of starch to one gallon of water being all that may be used for thorough saturation. It is hardly worth while to mention that to make a paste with starch, it is first saturated with cold water and then mixed with boiling water, four ounces of corn starch mixed with one-half pint cold water, and then briskly stirred and beaten with one-half gallon of boiling water makes a fine transparent paste.
Starch has been used in paste fillers for hardwood to keep the mineral pigments, such as silex, clay or gypsum, from setting hard in the package, but of course low priced corn starch is the favorite brand for the purpose. As much as 20 per cent of the total weight of dry material has been added of corn starch. It is also the dry material in the most favored brands of floor crack fillers that are being successfully used in private residences.