Tuesday, December 8, 2015

Backstrap Loom Weaving

Hello again everyone! I am recently finished with my doctoral training and in a new job and back to crafting again. Well... technically, this post's topic of weaving I originally started as a stress-relieving activity during the height of my studies. Weaving is meditative and creates satisfying, well-ordered structure in front of you with minimal mental gymnastics. At least if you're not making any complex fabric.

"Weaving" probably initially brings to mind images of gigantic, unwieldy, wooden looms taking up half of one's living room. And indeed, if you want the height of industrial efficiency, stylistic freedom, and ease of creating different finishes and textures, that's the way to go. But I was A) poor, B) didn't have 100 square feet to spare, and C) just wanted a relaxing craft activity. So I chose to use backstrap weaving techniques:

Backstrap weaving (image by Infrogmation, GNFL license)

Backstrap looms, like the one shown above, are cheap to make, requiring only cords, straps, a series of wooden dowels and slats, and some spare lengths of the same kind of yarn used to weave. The fabric you are making itself holds the loom together otherwise. When not in use, the whole project can be rolled up and stored. While in use, the loom is held together by placing tension on the warp yarns (vertical to the weaver) with your body, leaning back and stretching them between yourself and an anchor point in front of you. Dowels then keep the yarns separated while you weave the weft yarns (horizontal to the weaver) back and forth between. As you finish sections, you partially roll them up on the bar nearest you so that the next section is in reach, and so on until finished.

I didn't start with anything as ambitious as the woman above's yard-width cloth. I started by making a simple, thin, acrylic yarn strap. Below is a third party technical diagram of a backstrap loom, followed by a photo of my actual homemade one:

The warp threads are actually one continuous loop back and forth between the two anchor points of the loom, at the body and the far end. The warp threads can be seen splayed out at (A, furthest from the weaver) in the image. These tend to get tangled on their own, though, so to help prevent this, I made a "cross" (B) in the yarns by weaving a simple stick between every other thread, then weaving another one between the opposite threads (actual cross is between the sticks at B). This forces any tangles to resolve themselves and leave the yarns in order and well-spaced going toward the working section of the loom. To help keep the yarns spread out and untangled, tension is applied by the bar near the body (C), which is attached to a strap around the weaver's back (not shown, though notches are visible for the strap to attach). Two sticks are used here to allow the finished work to be rolled up as progress is made, without unrolling from the tension.

Then the actual process of weaving involves taking another length of yarn, the weft, and passing it through all the odd numbered yarns, then all the evens going the other way, back and forth. The weft thread is all rolled onto a bobbin (D, I used a knitting needle) so that passing all of it through the warps doesn't take an hour each time. The working edge of this piece of cloth is at (E); you can see where the weft has made it to so far. The stick right at the working edge is used to "beat down" the weft toward the finished cloth after each pass to make it nice and tightly woven.

How does the weft get between opposite yarns each pass? Well, you could thread it through each time manually, but that would be horrible. Instead, there's a system to quickly shift all the even numbered yarns up and then all the odd ones, quickly and efficiently. The odd numbered yarns are held apart by a nice thick bar (F) at the back of the loom. The even numbered yarns are then each individually tied to little strings ("heddles") that reaches down through the odd yarns, and then attaches above to a stick (G). To raise the odd yarns, the thick bar (F) is moved back and forth and up and down to well separate those yarns, while the heddle strings allow the even yarns to pass below without getting in the way. This creates a triangular space between (the "tent"). The beater stick (E) is placed inside (it is removed and replaced each pass), and flipped on its side to make the tent even bigger. Then the weft bobbin (D) is passed through. The weft is beaten down, and the beater stick removed again. Next, the thick bar (F) is pushed back out of the way, and the stick with all the heddle strings on it (G) is lifted, PULLING all the even-numbered strings through the odd ones so that they are now on top. The beater stick is put in again, the weft bobbin passed the other way. These two phases are repeated over and over again until a cloth is formed.

Above is the finished result of my first strap. If you look very closely, you can see several characteristic errors made by people who don't know what they're doing. For one thing, one end is about half as wide as the other. This is called "pulling in" and it results from not leaving enough slack in the weft thread as it is woven through the warp. When it gets beaten tight, the weft is crimped, and thus shortens. If there's no slack, this pulls in the sides of the whole cloth, making it progressively narrower. The way to fix this is to leave the weft at a slight angle before beating it tight, so that it is a bit longer than the width of the cloth, leaving room for crimping.

You can also see that at the edges, the texture changes in places. It becomes more square looking, while the middle of the strap looks hexagonal. This is because the warp yarns at the edges were looser than the ones in the middle. I didn't have even tension across my whole width. Thus, the warp and weft at the edges are about equally tight and pass over one another equally, while the warps in the middle are much tighter than the wefts, so one of them crimps and the other doesn't, leaving the hexagonal look as you can only see one of them. On the sides you see both warp and weft.  My next attempt was a lot better:

Here I was making a small patch of a twill fabric (specifically a gabardine). The first strap I made was a "plain weave", over under over under. In a basic twill, instead of having all the odd yarns alternate with the evens, what you do is pass over TWO warp yarns, then under two, then over two... Which two you pass also shifts over every time you send the weft through, like this:

Twill Weave (by Jauncourt, CC Attribution Share-Alike)

If you imagine counting off every warp thread as 1,2,3,4,1,2,3,4... this means that depending on the pass of the weft, you need to variably lift all the 1's and 2's, then next all the 2's and 3's, then 3's and 4's, and finally the 1's and 4's. Four different sets of yarns need to be controlled instead of the two sets for the simple strap I made. This means that I need not just one thick bar and one set of heddle strings, but instead one thick bar and THREE sets of strings. This way, I can achieve all four types of lifted sets of strings. You can see the three different tied sticks in the photo above. This is trickier to set up, but not much trickier to weave. I'm using orange yarn for the warp this time, and red for the weft, so that you can tell them apart later.

Here's one side of the finished product (above). Notice that you can ONLY see orange. This is a "warp-faced" fabric since on the intended display side (above), you can only see the orange warp yarns. The red wefts are hidden underneath. Notice also that the cloth looks much denser and tighter than the strap earlier. Since the yarns aren't crimping as much as in a plain weave (only every two yarns not every one), more yarns are packed into a square inch than in a plain weave. This makes twills harder-wearing and popular for work clothes and jeans. The tight weave also makes twills more insulating (jeans are generally warmer than linen pants, which use plain weave), and easier to waterproof. Gabardine, the weave I made, is popular as an outer weave for raincoats, for instance.

Here's the back side of the same cloth. On the back, you can see the warp and weft about equally well. This is not the "face" of the cloth, though, so it's still called "warp-faced." Notice that the width doesn't change quite as dramatically as last time, but I still pulled in a bit from start (left) to finish (right). The tension is more even this time. The edges are also more consistent, from repetitive practice.

Next, I used a mixture of stiff hemp warp strings and soft acrylic weft yarns, and chose a new pattern: a diamond twill. This is a normal twill, but with the pattern simply changing direction in blocks. When tying the warp strings, I changed the pattern partway, and I also changed the direction of which heddles I lifted occasionally while weaving to make the pattern change the other way as well. Here's the loom set up first, followed by a diagram of a diamond twill.

If you look closely, this looks just like a normal twill but in smaller "blocks" that flip occasionally.

Again, this pattern required 4 types of yarn lifts, so a bar + 3 heddles, varying which sets of warp yarns were lifted as I went. The finished product is below, with a bit fancier finishing of the ends. You can see the diamond pattern, though it's not a consistent looking as I'd like. You can see both hemp and red yarn here, because even though it's warp-faced, the yarn is so much bulkier that this balances out the tension visually and keeps them both more equally visible at once. Notice that when I cut the bottom, it by no means immediately unravels. These cloths could definitely be cut to patterns and used in sewing if large enough.

It takes me about 20 minutes to wind the warp yarns around two pipes in a wooden board and transfer them onto the loom, then anywhere from 30 minutes to hours to tie the heddles depending on complexity and width of the cloth, and about 5 minutes per inch of cloth to weave the weft along. Next up is going to be attempting a much larger piece of fabric, like a dish towel, perhaps. I also want to try out changing the warp and weft colors across the fabric, such as when making a plaid fabric.

Much fancier and irregular patterns can also be woven into a cloth, like the shapes of animals, but this requires manually "dropping" or "picking up" yarns in violation of the background pattern as you go, and it is very painstaking by comparison to plain fabrics like these.


  1. Nice to see you back, this does look quite interesting and is probably something I will try myself soon.