How is Jacquard Weaving Different?
This question comes up frequently. Because of the single thread control of the hooks on a Jacquard head, it presents a unique opportunity to weave complex fabrics. There is a dichotomy with the Jacquard loom – for all of the design variations possible with this loom, it is a loom with many constraints that need to be addressed by the weaver.
Let’s start with weaving a basic tabby.
Begin with a 4-shaft loom with treadles. The loom is threaded in a straight draw and a tieup is designated 1 & 3 and 2 & 4. The weaver inserts weft by pressing treadles 1 & 2 in alternation.
Now, let’s do this on a dobby loom. We keep the straight draw on 4 shafts. The dobby mechanism replaces the treadles, so we need only a lift plan with 2 rows – one with all odd numbered shafts rising and one with all even numbered shafts rising . The weaver inserts weft while advancing the dobby mechanism which repeatedly weaves our 2 row sequence. The liftplan can be represented as a mechanical lag chain, a punched paper tape, or in electronic form where each rising shaft is represented by a pixel in a file.
And on the Jacquard loom? The Jacquard loom has only the single harness with at least one heddle attached to each hook. The heddles are threaded straight across out of the cross. Jacquard designs are based on a “point paper” concept. Point paper was originally fine graph paper where each rising warp was indicated with a black square. Today’s software creates a virtual point paper by using an electronic file with pixels – each pixel representing an intersection in the fabric. A black pixel signifies that the warp end is raised at that intersection. The point paper for our tabby will have as many squares in width as there are hooks in the head. The first row will have all odd numbered threads blackened for lifting. Row 2 will show all even squares in black. The control of the Jacquard head will be either punched cards or an electronic file. Either 2 cards or a file with 2 rows will suffice to control the lifting of the correct warp threads So far, so good – weaving tabby works easily on all three looms.
Now let’s try a rather simple combined structure - tabby/2/2 twill combination.
On a 4-shaft loom, this is not possible. Mixing twill and tabby requires 6 shafts. If two additional shafts can be added, twill is threaded on 4 shafts and tabby on the remaining 2. The tieup requires that 3 shafts lift for each treadle, 2 for the twill and 1 for the tabby. The density of twill and tabby are also quite different – twill needs a closer sett and has a different rate of takeup. An easy way to bridge this is by threading 2 tabby warps in each reed dent, and 3 warps per dent for the twill portions. By hand throwing the shuttle and maintaining a beat determined by the weaver, the takeup rates can be evened out.
On the dobby?
The 6 shafts should definitely be available. Threading will be a straight draw based on structure for the designated area. The liftplan will now have a minimum of 4 rows to accommodate the 4 twill picks, which will also lift one of the two tabby shafts with each pick. And the varying density? If the dobby is a hand operated dobby in a weavers’ studio, of course the reed can be sleyed the same as for the loom with shafts/treadles. On an industrial dobby, warps are beamed several hundred to several thousand yards long and sleying unevenly is not as easily accomplished if the warp has been wound sectionally and at an even number of ends per inch, though it could be done.
Our Jacquard loom presents interesting challenges. Threading a pattern is no longer necessary. Sleying the reed could be done unevenly, but it will not be as effective because the heddles on the Jacquard loom are evenly spaced. Setting up for the mix of tabby and twill would be very time consuming. Since the heddle spacing on the Jacquard loom is fixed – at least for the length of the warp – cramming dents in the reed will cause odd tensioning in the warp. There is a major issue with this cloth – even though the setup seems easy. The takeup on plain weave and twill is uneven. In an industrial setting, at 300 or more picks per minute, this takeup difference could make some warps so tight that they begin to snap and bring the loom to a halt.
What about weaving images and pictorial designs?
The 4-shaft loom is able to do rather complex geometric patterns, such as overshot, by utilizing blocks of pattern combined to give an overall pattern – very often using supplemental weft to show the pattern. Simple lace weaves and fancy twills are no problem. The setup of this loom requires a specific pattern threading and treadle tieup to produce the desired design.
The multi-shaft dobby does more blocks and can now produce blocked images with rather simple forms. The dobby, with no need for a tieup can accommodate many variations of threading and produce very intricate liftplans that vary the treadling. Only the threading is static – the liftplan can create nearly infinite variations. All of the capability of the 4-shaft treadle loom is possible as well.
The Jacquard loom has radically different capabilities. With a simple straight threading and each thread controlled by an independent “hook” there is no more designing with a threading, tieup and treadling. All that is left is a design surface that can be represented by graph paper or a bitmap file. To weave imagery, the image needs to be reduced to a limited number of “colors”. The image width is then sized to fit the number of threads on the loom – 1 pixel per thread. A set of weave structures is selected considering their compatibility in terms of takeup and a structure is assigned to each color. Two very common choices are 5-end or 8-end shaded satins. Where an 8-end satin is usually 1end up and 7 down, the shaded variations include 1-7, 2-6, 3-5, 4-4, 5-3, 6-2, 7-1 which provide 7 different shadings of a two color contrast. That selected structure is then overlayed on each area of corresponding “color” – either by hand on point paper or electronically with CAD software. Prior to weaving, a float check must be made to avoid threads producing excessively long jumps and the edge contours are checked for their effects – it is possible to adjust the meeting of differently structured areas to either have a sharp or a diffused junction. If there is any need for selvage treatment, it is also put into the bitmap file for weaving the cloth. On an electronically controlled Jacquard loom, the file is put on the control computer and weaving begins.
This is only the beginning – the preceding description applies to a one warp, one weft satin damask. It is also possible to utilize multiple warp and weft systems for dithered doubleweave images that look much like newsprint photos blown up – or exquisite doubleweave fabrics with intricate patterns. Taquete and samitum can be used in a “painterly” fashion when 3 or 4 weft colors are used. Jacquard looms can produce pile weaves, multilayered cloth, complex upholstery type fabrics and much more.