Another important point in designing for gauze is that if the texture of the solid cloth is loose and that of the gauze pretty firmly twisted, the take-up of the warp may be very different when weaving. To avoid this the gauze and figure should be well intermixed, and not be in too great quantities in any one part—in fact, the gauze and plain should be constantly interchanging, and when the pattern is such that this cannot be, the textures must be regulated so that there will be about an equal quantity of warp taken up for each. A little practice will soon show this.
Nothing has been said about the description of jacquard used for working gauze, but the same principle holds good as for working with shafts. A gauze shed is taken to be a plain jacquard lift—that is, the shed formed by the single-lift jacquard raises the yarn and lets it down again before beginning to raise the following shed. This enables the doup and doup yarn to fall into their places before being drawn away to form a following shed. At the same time, we are not limited to a single-lift jacquard. If you have a double-lift jacquard, and want to work a small piece of gauze, do so; but do it correctly, or, in other words, take means to make a good job of it. Before explaining how to do this, it will be well to show where the difficulty exists. In a double-acting machine one griffe is rising when the other is falling, and in plain gauze the doup standard and leash carrying the crossing thread are raised alternately, one shot being thrown into the shed formed by each. Therefore, the same thread is up for every shot, and the thread round which it twists is always down. Now, when one griffe has raised the doup standard and the next one raises the leashes carrying the same threads, both will pass in the centre of the shed, and, as shown in [Fig. 147], the crossing thread will be dragging up the lying thread from the position shown by the under dotted line, thereby causing considerable friction on the yarn, which must be detrimental to a fine or weak warp, and is inclined to drag the doup through the eyes of their standards; but as the harness in coming to the centre slackens the warp threads, and also as the slackener begins to act when the harness begins to rise, the threads will be further slackened in those sheds where the doups follow the back leashes, and this reduces the friction. It may, however, be entirely avoided by raising the lying threads to the mid position to meet the descending griffe, and then let down with it. A simple method of doing this is to have the leashes carrying the lying threads through a separate slip of cumber board at the back, and knots on them above it, so that when it is raised all the lying threads will be drawn up with it.
The cumber board can be raised by a cam, or in any other suitable way. (See Journal Weaving for Scotch Carpets.)
Fig. 147
These leashes might also be raised by means of a shaft through loops in them, or with bars under the jacquard hooks, in the same way as is done in twilling harnesses (which see), but with a special motion to raise and lower them. In [Fig. 147], the dotted line A, B shows the middle position or centre of the traverse of the yarn in shedding.
Although this is the proper means to adopt to work gauze satisfactorily with a double-acting jacquard, or with any double-acting shedding motion, it may be that small portions of gauze, such as a few stripes up a web, are wanted without the trouble of making any special arrangements for it. Good strong twist cotton yarn will work very well, if nicely tempered, in a double-acting machine. The slackeners can be arranged by leaving a few hooks apart to work them with, and cords tied to these hooks and let down at the back, in the same manner as in the gauze harness ([Fig. 138]), which will do very well. When three or more shots are thrown into each shed of the gauze—that is, between the crossings—there will be much less friction than when the crossing takes place at each shot, as it is only at the crossing the friction takes place.
One source of annoyance in working gauze is the wear on the doups, which requires them to be changed frequently and adds cost to the production. It has often been attempted to work the gauze by other means, and for some classes of work this has proved successful. One of the best arrangements, and one that is largely used, is the gauze reed, which is almost entirely adopted about Glasgow for weaving leno curtains in the power loom; it is also employed for other classes of work, but is limited in its use. It will not supply the place of a gauze harness.