color.

A very consistent size will make the preparation of colors extremely difficult, as they need a double quantity of gall for the purpose of spreading out. If there is but one color used, the preparation on such a size would be possible without spoiling it, but with four colors this is entirely impossible because the repeated drawing off of the colors, which always leaves particles behind, will, by and by, impregnate the size so that when the fourth color is prepared the first will not spread out any further.

The more the impregnation of the gall and size increases, the power of expansion of the colors decreases and this continues until both materials are useless.

It is therefore advisable, as I have already stated, in the chapter upon the varieties of sizes that the colors should be prepared separately on a small part of size to determine the correct consistency of the latter and to prohibit the whole size being soiled.

The gall should be kept in a small bottle containing about 1/10 quart with a perforated stopper from which a small tube protrudes and from which the gall can be added to the colors in drops.

Although the preparation of the color in this way takes more time, this trouble is amply repaid by the result.

Fatty bodies are injurious to the size, therefore they must be carefully avoided because they have the same effect as the gall, they form, although not insoluble in water, a combination with the size and prohibit the colors from spreading out. Fatty bodies can be transferred by glutinous fluids into a state of the most minute division and they then form emulsions.

Natural emulsions are milk, the yolk of egg, and the milky saps of plants. For this reason, in many establishments raw milk is used as a propelling medium for hair-veined edges.

There are also fatty bodies which, in an artificial way, form an emulsion even with water; for instance, almond, poppy and hemp, if they are ground to a pulp with a little water yield a milky mixture. All these emulsions artificial as well as natural, can be employed as expanding mediums and give better results for marbling than petroleum or naptha.