The preparation of the colors is carried on separately on a small part of the size, so that the whole quantity is not rendered useless. If the colors are rightly prepared in proportion to their expansibilities in relation to each other, the new size is to be poured into the trough and the marbling may begin.
The mistake which is commonly made in marbling is, that too little attention is paid to the size and color. Frequently the size is soiled and the colors are spoiled by adding too much gall before an edge is produced. For this there are generally three causes, either the size is too fresh, too thick or the colors have been prepared on the same size by which the edges are to be produced.
Each size which is boiled should only be taken into use after perfect cooling and after several hours have elapsed, since in a warm state it would not permit the colors to expand even by adding a large quantity of gall. Only after the expiration of ten or twelve hours after boiling will it have the correct quantity of mucilage and then only the size possesses its full value. This time having elapsed, the size is filtered through a cloth and is then ready for use.
A size when too thick, allows the colors to expand only with great difficulty and demands a three fold larger quantity of gall than when it possesses its normal consistency. It is very difficult to remove from a too consistent size the remnants of colors.
They always unite with the size and in this way the size not only becomes soiled but it is impregnated with a large quantity of gall. As I said before, the colors should always be prepared on a separate size which can be poured into a flat vessel as it is nearly impossible to prevent several drops of color sinking to the bottom.
If this precaution be taken and if the colors are prepared according to their relative expansibilities as they are used in the order prescribed, the process will not meet with any obstruction or difficulty. As the size plays such an important part in marbling, great attention must be paid to its preparation if it is desired to make a good base for the colors. I especially recommend to laymen that they direct their attention to the consistency of the size, as this is always the key to the production of good edges.
The different peculiarities of the varieties of sizes, viz; evaporation, influence of temperature, starry formation of colors, formation of angular scales in comb-edges, and all other things which have influence on colors, will be treated of in a special article on the varieties of size.