This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol2", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The Luxfer Prism Syndicate Ltd. have introduced a fire-resisting glazing, by means of a patent process of mounting or uniting glass by copper electrically deposited. The glass is assembled on a table with copper ribbons until a plate of required size is built up. This is then put into an electrolytic bath, and copper is deposited over the edges of the glass. This deposited metal is so intimately connected with the edges of the glass that glass and copper become practically welded together. It has been tested by the British Fire Prevention Committee up to 10000 Fahr., when 317 squares out of 324 withstood the action of fire and water.
Panels composed of pieces of glass leaded together are termed leaded lights, and may be either of plain, coloured, or mixed glass.
The leads should be pure vice drawn, with soldered joints. The lead is first cast in short cames, and then put through a compression vice to reduce it to the required size, polish and harden the surface, and mills the heart of the lead, so that it holds the cement and glass firmly. The compression of the lead protects it from the weather. Leads drawn in a molten state are softer than those compressed in a vice, rougher and less homogeneous, and rapidly corrode.
The leads or "cames" are of an H section, the stout middle portion being called the heart and the sides the leaf. The leaf may be from 1/8 to 1 inch in breadth, the heart being stout in proportion. For general external glazing, the leaf should be from 1/4 to 1/2 inch wide. Cames are made of many gauges to suit different thicknesses of glass.
There are three forms of leaf: flat, round, and beaded edge. Of the three, the beaded edge is preferable for general work, as it is more water-tight, whilst the broader leads are used for the outside margins, and should fill the rebate and project \ inch beyond.
Plain square lead glazing should be arranged in panes not less than 7 by 5 inches, with leads 7/16 inch wide.
When glass is inserted in windows for the purpose of creating decorative effects, rather than for giving light, the method of its insertion is much the same as for plain lead glazing, which has just been mentioned. The glass is cut to such shapes as are necessitated by the pattern, and is enclosed in the cames, which are soldered together where they meet, so that the whole is built up into a framework, and itself enclosed in an outline of lead came. It is usual to build up a window in this way in sections, which are slipped one by one into grooves formed in the masonry outline of the window, where they are afterwards cemented in. The sections are also soldered together, and attached to the saddle bars as afterwards mentioned. The fixing can, however, in smaller windows be made more satisfactory by means of a wood frame, a small bead or fillet being screwed on to the outside, so that there is no necessity for slipping into a groove, with the resulting vacant space to be filled with cement. After the glass is inserted, and at least a week before fixing, the cames are carefully cemented by brushing under the leafs a cement composed of oil mastic, or whiting and red lead, the leads being afterwards coated with blacklead so as to ensure their being water-tight. For the sake of strength and water-tightness, the glass should fit accurately to the heart of the cames, which can only be done with great care; but a window built up in this fashion is necessarily composed of quite small pieces of glass, and as a natural result it is structurally weak, and liable to be blown in during a gale of any strength. In order to prevent this the windows are stiffened by means of iron or copper "saddle bars," as they are called, passing across the window from side to side at intervals of about 18 inches, and, if necessary, - that is, if the window be more than 30 inches wide vertically, - from top to bottom. These are usually placed outside the window, but not necessarily so, for sometimes they are found inside, and sometimes on both sides. As a rule they are straight, but this is not essential, and in fact it is by no means uncommon to bend them to the shape of a head, or other object in the design. The windows are attached to these saddle bars by means of copper wire soldered to the cames and twisted round the bars; and the different sections of a large window are made to space with the saddle bars, upper and lower sections being in this way attached to the same bar.
It will thus be seen that all ornamental glazing is limited, in the matter of design, by the presence of these stiffening bars, and by the necessarily small pieces of glass which are used. These, however, can be cut to any required shape, though it must be remembered that when a window bulges under the force of a gale, it is the awkwardly shaped piece of glass which will first break. The design, therefore, is controlled by the fact that there must be strong outlines of lead appearing across and across it in all directions.
A further controlling influence is the nature of the glass which can be used. At the present time we have many good varieties of white and coloured glass, the coloured glass of a single tint being known as "pot metal," and being made by mixing various metallic oxides with the material of which the glass is composed. This is obtainable either in flat or graded tints.
Painted Glass is quite a different thing. It consists of a light pot metal, upon which paint has been applied, which itself consists of oxides mixed with powdered glass and some form of gum to make it adhere. The sheet upon which it is applied is placed in the furnace a second time, and heated to a red heat, when the paint is absorbed into the surface of the original glass and henceforth forms part of it. The paint is, as a rule, applied by means of brushes of a stiff kind, somewhat as in oil painting on canvas; but there is another form of tinting glass, known as Grisaille, which consists in laying the colour in thin lines across and across the surface to be tinted, so as to allow a considerable amount of light to pass in through the meshes. Deep tones of simple colours are not always obtained by selecting a deeply coloured glass, but often by introducing two or three sheets at a particular spot, using, of course, a thicker came for the purpose.
It is not the intention in this book to go much into matters of taste or of design, and the illustrations have consequently been chosen mainly for constructional reasons. Fig. 232, for instance, represents a long
Plate VI. East Window, Church Of St. Matthias, Barbados narrow panel such as could be easily built up, the saddle bars, if any, occurring above and below the coat of arms, which has been designed to occupy a rectangular panel.
By Cakebread, Robey & Co., 86 High Street, Stoke Newington, London, N.
Fig. 233 illustrates a large window, made by Messrs. Cakebread, Robey, & Co., for a wood frame, mostly in small squares, needing no support, though the middle panel at the bottom would be the better for one vertical stay bar. Its presence, as a shadow on the glass, would not materially interfere with the symmetrical design.
Fig. 234 shows ornamental glazing as applied to an ordinary sash window, for execution in carefully selected pot-metal only, not uniformly tinted in each piece, but chosen for its markings. It will be seen that in each sash there is a nearly horizontal line of leading right across, which a saddle bar could follow with a small amount of bending.
Plate VI. is a small example of what can be done with lead glazing in painted glass. It represents a window carried out by Messrs. Cakebread, Robey, & Co., of Stoke Newington, and erected in a church in Barbados. The sky and some portions of the border are in pot-metal, but most of it is in tinted glass carefully painted. The leading is carefully devised so as to accentuate the design, which might otherwise be easily broken up and spoilt - and the saddle bars follow the leading, one, for instance, passing over and round all three heads in the middle light.