Interesting effects happen when you weave boundweave with three colors on four shafts/sheds. Because of the mismatch in number of shuttles and number of sheds, the colors will automatically shift position every time you rotate through the pattern. This technique is sometimes called the Navajo Saddle Blanket technique (for example in Clotilde Barrett's Boundweave and Mary Atwater's Shuttlecraft Book of American Handweaving).
The Structure
In twill weaving, the weft threads pass over and under multiple warp threads at a time (instead of one-by-one, as in plainweave). This allows the threads to pack together tightly, which explains why twill shrinks so much more than plainweave when it is taken off the loom.2/2 twill cycles through four treadles on a four shaft loom. Here are the four different possible picks in 'rosepath' threading:
2/2 twill can be woven as boundweave by using a wide warp sett and packing the weft picks tightly together. In essence, it takes four picks to cover all of the warp threads and thus make the appearance of one solid line across the fell edge of the weaving. Below is what those four picks look like, combined, in cross-section. Note that each warp thread has two weft threads above it and two weft threads below it, which is all part of being a "2/2" twill. The colors will show up in different places on the front and back of the fabric, but otherwise the structure is identical on both sides. As a result, this type of boundweave will not have any significant curl.
Because that single line is made up of four picks stacked on top of each other, it will make a slightly sinuous wave rather than a perfectly straight line. Here is an illustration of what it looks like, with that wave slightly exaggerated:
The look of the weaving changes as more and more rows are added, due to the way the threads pack together and overlap in boundweave. Only the weft floats that pass over two or more warp threads will actually show up in the pattern. Whenever the weft passes over just a single warp thread, it hides under the loftier floats packed in around it and ends up completely disappearing. Here you can see that starting to happen:
What shows up on the face of the fabric can be thought of in terms of the spaces between the warp threads, rather than the threads themselves. A weft float over 3 warp threads actually covers 2 spaces, while a float over 2 warp threads covers 1 space. When the weft covers only one warp thread, it covers no spaces at all.
In order to visualize how a 2/2 twill draft translates into a boundweave pattern, it may be helpful to think of the weft threads covering the spaces between the warp threads rather than covering the warp threads themselves. A weft float over 3 warp threads actually covers two spaces, while a float over two warp threads covers just one space. If the weft covers only one warp thread, it covers no spaces at all. This translates exactly into the proportions in the resulting pattern. Weft threads covering 3 threads (2 spaces) are twice as long as weft threads covering 2 threads (1 space). Weft threads covering 1 thread (zero spaces) are not visible.
The image below shows the same twelve picks as the image above as they would appear with a properly firm beat for boundweave. The warp is covered entirely, and so are the weft threads that pass over just a single warp end.
The draft
A traditional draw-down does not accurately represent the pattern that results in boundweave. Weaving drafts usually represent balanced twill, where warp and weft have an equal presence. The weaving shown in the two images above would be represented like this in a traditional draft (read the treadling directions bottom-up):
Although it tells you exactly what to do very clearly, the draft above doesn't give you a good idea of what your weaving will actually look like. Below is a modified draft that does a better job of visually representing the results.
Each four-pick sequence (1-2-3-4) that produces a solid line of boundweave is condensed into a single row in the treadling directions, which should be read left-to-right starting at the bottom. The draw-down has been modified to represent the resulting pattern: the hidden singles are eliminated, 2-thread floats are represented with one unit, and 3-thread floats are represented by two units. Two full repeats are shown, which amounts to 24 total picks.
While more accurate, the draw-down above is still necessarily pixelated. The image below gives a better sense of what the weaving actually looks like. Three full repeats are shown (36 picks).
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