black and Indian red to a proper tint. This must be scumbled or spread very thinly in the forms that it is intended that the veins should take. In relation to the formation of marbles, it must here be observed, that they are beds of rock that are veined by metallic or other substances running amongst them, and that the veins always run in the direction of the strata, precisely as thin streams of water would if poured upon an inclined plane, such as the top of a table slightly raised on one side. If this experiment is tried it will be found that the streams, if they commence regularly, will, from some inequalities of the surface, soon alter their course and turn in various directions, sometimes joining together, forming a sort of star, and then spreading into finer threads, while others will join and form a thick vein, but still running in various forms towards the bottom. This is precisely the way in which the various substances spread themselves on the limestone, of course penetrating the surface and interspersed with the strata.
From this experiment the painter will see that however the direction of the veins, they must all appear to be traveling to the same point by different roads and nothing can be more contrary to nature than those violent and eccentric breaks which painters of veined marbles usually practice. This will apply to all marbles except Porphyry, Black and Gold and Florentine.
The first broad vein of the marble having been rather faintly painted, the veins nearer the surface are next to be put in. They are made a little darker by the addition of black and are to be drawn very thin, taking the direction of the broad faint vein and being divided according to previous studies from nature. The veins which are nearest the surface must, of course, be darker than the others, and the color may be darkened and warmed by the still further addition of black, with a little lake and blue. This vein should be drawn with a fine sable pencil very thin, and made to take nearly the direction of the last veining. Only
