Peinture et Appret. For painting 011 a single sheet of glass, the following rales must be observed.
A pure white glass must be chosen for the purpose, free from air specks or bubbles, and especially difficult of fusion, as the whole labor would lie lost ii it were attempted to bum in the colors upon a ground which fused as easily as themselves. It is practicable, as the examples of the ancients show, to paint on what would appear the commonest glass with a good result, provided that it does net contain too much lead, and thereby become too easily fusible.
Before the operation of painting, the glass plate must be rubbed to a sutficient extent with pure lime, slaked by exposure to the air, in order to clean it perfectly.
The ground or foundation must then be laid over the whole surface of the plate, which may be done in two different ways. Some artists simply dip a piece of clean linen cloth, or a Hat camel-hair pencil, in oil of turpentine, and brush the pane of glass with it equally over its surface , while others give to the whole a thin clear ground of black glass-painting color, in such manner as not to destroy its transparency, but at most to give it the form of a dead ground glass. Both methods answer the purpose of covering the glass with a viscous surface, which takes the design and the colors better than a polished ground ; the latter prepares the glass at the same time for the painting effects which are to be obtained upon it.
In both cases the ground which has been laid on must be most carefully leveled over, and brought to as thin a coat as possible with a large hair pencil, and must be driod quickly, taking great care to preserve it from dust, etc.
Painting on one sheet requires only one pattern drawing or cartoon, which, however, may be used in two ways. Either the glass sheet, grounded and dried as above directed, may be laid upon the drawing, and the ourlines, as seen through the glass, traced lightly with a fine pencil, and with black or other glass color corresponding to the ground. Or the drawing mav bo placed reversed on the sheet, and all the outlines marked ovvr with a steel or ivory style. If this latter method is used upon a ground ot simple turpentine, the back of the drawing must previously be rubbed over with black lead, so that the traced lines may appear dark on the light ground.
In botli cases, the drawing, whether it is placed upon or under the glass, must, for the sake of convenience, be fastened to it with pieces of wax at the four corners.
For properly carrying out the process of laying on the colors, a desk or easel is necessary, which should be capable of being placed in an inclined position by means of props, and should be formed by fixing a glass plate in a wooden frame, so that the light may pass through the painting. Sometimes during the progress of the work, the glass which is being painted may be removed from the easel and laid upon a sheet of white paper, in order better to show the effect of certain colors.
The vehicle with w hich the pigments are laid on is generally oil. Some artists use exclusively water, but this alone is an insufficient medium for binding the metallic bodies to the glass, particularly if, as in the case of fused colors, they are somewhat coarse in their nature, and require to be laid on in thick layers. They then easily loosen from the plate before the firing, and render the process of laying on much more difficult. It is an important advantage, that with oil the edges are more sharply defined, and the parts already painted may be again touched over when dry without danger of loosening the ground.
It must be understood that when it is wished to make use of water, the plate must either not be grounded at all, or only with a glass-painting color worked up with water.
The most suitable kind of oil for the purpose is rectified oil of turpentine, soinew hat thickened by standing, and to which a little oil of lavender is aided. This preparation gives the mass the ncccssary degree of viscosity, and also prevents the color on the palette from drying up and thickening too quickly.
The palette should be of thick sheet glass, ground rough by rubbing with a glass muller and fine sand.
Preparatory to mixing with oil for laving on, those colors which require a ®*x must (unless a different process is specially indicated) lie ground fine in water with the flux, and again dried.
But the fused colors, i. e. those in which the oxide has already t/7T7v thrill - UigiircUU uy n/uCrui>Oll vt!/
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