This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
41. These are plain basket patterns, and can be made in any size iron and set to any mesh. The frame is of angle iron, the ends of the meshwork being riveted to it. The meshwork grilles, being of an interlaced pattern, form a strong and economical screen to manufacture. If the surface to be screened by this basketwork is considerable, it is desirable to run a line of rivets at intervals through the mesh; otherwise, the metal strips that form the mesh are likely to slip out of place and become distorted. If a more ornamental grille is wanted, the simplest variation is secured by twisting the bars as shown in Fig. 42, the result being that a mesh is produced with the edges towards the eye and a series of flat crosses at the intersections. If a border to the grille is desired, the scroll ornament shown in Fig. 43 is suitable and inexpensive. A glance at the illustration will show how this is made, by turning the ends of each strip or bar. In this case an angle-iron frame could not very well be used, because part of the scroll would be hidden by the flange of the angle. The frame may be a flat bar, though a small channel would be preferable, as the ends of the rivets that fasten the scrolls could be hidden in the hollow of the channel.
35. A great variety of grille designs have the square meshwork shown in Fig. 42 as a basis, with additional ornament introduced at top and bottom, as shown in Fig. 44, or with a border and center ornament, as in Fig. 45. It will be seen that the ornament is formed to a great extent by turning the ends of the bars forming the square meshwork into scrolls, and adding other scrolls as may be desired. This can readily be seen by examining the designs shown, but to make it perfectly clear, some of the component parts of Fig. 44 are shown separately. The small top scroll a is shown separately at (b); the large central scroll b is shown at (c); the central division and loop c is shown at (d); and the small scroll and ribbon d is shown at (e). These are all made of single pieces of iron. The pattern shown in Fig. 46 is designed to produce a diaper effect, as is also Fig. 47, the latter being a more open pattern. These designs are all for grilles of light strips not over 1/16 inch thick by 5/16 inch wide, though at times heavier material may be employed. Figs. 48 and 49 are radiating designs suitable for arched window or door openings, but in other respects are precisely the same as the above described. At Figs. 50 and 51 the square mesh is abandoned, and the metal is made rather heavier, so that the long straight bars may be strong enough to resist the tendency to bend. There is no set rule for determining the size of iron of which a design should be composed, as this is governed by considerations of artistic fitness for the position for which it has been designed. If the iron is too thick to be readily twisted at the intersection, it may be half checked, as shown in Fig. 52; or, if one piece is wider than the other, the wide piece may be punched out to permit the narrower one to pass through it, as shown in Fig. 53.