This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Cutting The Glass. The cartoon having been placed upon a table, the glazier lays upon it a sheet of glass whose color is decided by the artist and by him outlined in white or some other color. The glazier then cuts it with a diamond, taking care, among other things, to leave a space between each piece of glass, determined by the thickness of the interior of those strips of lead by whose edges the pieces of glass are afterwards united.
Leading. The strips of lead, a section of one of which is shown in Fig. 81, consist of two narrow ribbons joined together lengthwise, by a narrow strip of the same metal, running along the center. The cartoon, according to which the pieces of glass have been cut out, is also used for putting these pieces together and leading them. Beginning as nearly as possible in the center of the picture, the glazier works outwards from the center in each direction. When the first piece to be fixed has been laid in position, it is fastened in several places by pegs driven into the table. These pegs, or nails without heads, fulfil this purpose by aid of small pieces of milled lead, laid between the pegs and the glass. One of the sides of the glass is then enclosed in a piece of lead. When this strip of lead has followed the whole outline of the glass, pressure being, at the same time, applied, the superfluous breadth is cut off with a lead knife. A second piece of glass, placed like the first with pegs until the strip of lead is fixed on, is then put in place. The edges of the lead are then pressed down, and this operation continued until the panel is finished.
196. Glass embossing is a description of ornamental glass having nothing in common with the art of glass painting, but frequently and advantageously employed as an auxiliary to stained-glass decoration. Generally used for overlaid glass, that is, white glass upon which a coating of color has been flashed in the blowing, it consists of a kind of white drawing upon a colored ground, obtained by removing the coating of colored glass where, according to the drawing, it is intended to lay bare the white stratum. The process of engraving requires that the glass be first covered with a coating of linseed oil boiled with litharge, to preserve from the action of the acids those parts not to be acted upon. This layer is then dried in the drying oven, and the varnish removed by means of a graver or needle and a scraping instrument from those parts where the glass is to be acted upon by the acid. The plate of glass is next laid horizontally on a table and a raised border of wax carried around the edges of the glass, upon which the acid is then poured. The acid is allowed to remain on the glass as long as it may be required to destroy the colored stratum wherever exposed. This operation completed, the glass is washed and freed from the borders of wax and the wax ground. The cleanliness and firmness of the engraving are then in proportion to the thinness of the coating and the diluted state of the acid. If very much concentrated, the action of the acid extends over the etching- ground and seems to undermine the lines.
Fig. 82 presents a door panel of white glass flashed with any one color, which may be vitrified or eaten away by the aid of hydrofluoric acid until it shows the base or white surface only, thus rendering a beautiful effect, rich in appearance and clear in definition.
Fig. 83 represents a similar panel, with a design from nature, and may, like the preceding, be worked on white, blue, or orange glass. This design may also be embossed on simple white glass by drawing an exact outline of the size required. Placing this underneath the sheet of plate glass, take a sable pencil and paint in the background carefully with Brunswick black and turpentine, accurately tracing the lines of the design and keeping the glass rigidly free from grease or grease spots. When this glass is ready to receive the acid, fix the wax around the edges and pour the dilute hydrofluoric acid quickly over the surface, allowing it to remain until the design required is sufficiently etched. Then pour off the acid, wash the plate freely and remove the wax. This wax is composed of three parts beeswax and one part Burgundy pitch, fused together and forming a soft putty, resisting any acid.