l)Oon vitrified with the flux into the state of a transparent glass, should for the purpose of laying 011, only bo coarsely granulated; for the finer these are ground the more likely is their transparency and perfection to be impaired w hen burnt in.
Those pigments which are laid on in their simple combination with an earthy vehicle, and without flux, as for example the yellow and red colors prepared from silver, form an absolute exception to the use of oil, and must, for laying on, be stirred up with water to the consistency of a thick cream
The first of these three kinds of pigments should, as a general rule, be laid on in a thin, the latter two in a pasty, state. The depth of tone of the color depends, w ith all three, upon the degree of thickness in which the pigments are laid upon the glass.
The laying on of the fused colors is accompanied with more difficulty than that of the other kinds. The latter are simply laid on with the pcncil, in the same manner as with other kinds of painting, and the only care necessary is that the coat may be perfectly even and regular, therefore for large surfaces a wide smooth pencil or driver is usually employed. The colors prepared from silver must be treated differently, and laid on the gla^s at least to the thickness of the back of a knife.
But the fused colors must be brought upon the surfaces to be covered in the state of a thick flowing mass, moist enough to run, but consistent enough to lie upon the glass. For this purpose small jiortions must be laid on and spread out w ith a pencil or small spoon, and made to flow to the circumscribing outlines, by inclining the sheet in the proper directions. If any part of the surface thus covered is require 1 to take a darker tone of color, the plate must be kept for some time at an inclination in the corresjKJiiding direction, so that the color may thus accumulate thicker on that part. By this process many gradation* of tone may be obtained from one and the same pigment.
The remaining rules for the laying on of the pigments aro those which principally result from the different methods of pamting on one sheet, of which there are principally three.
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