Tuesday, April 29, 2014

Weft tension: how to control the amount of weft used in tapestry weaving

The Latest Catastrophe

I often get questions from students similar to the one I found in my inbox this morning. I thought some of you might be interested in the solution to this common problem.

The student started the email with, "Hi Rebecca, Here is my latest catastrophe. I am so discouraged."

She went on to say:
I think it is a tension problem. I am currently weaving pick by pick.  There are exactly the same number of rows of weft all the way across!!!  So what the heck is going on?  You can see the left side is packed way tighter, but that’s not the answer.  And it makes it look even more weird.  I need to sort out these issues or I think I won’t have the confidence to weave at all.  There is so much time invested to just throw something away.  I so much enjoy the process of weaving but I want some confidence that I won’t have to throw all my projects away.  I so hope you can help me.

The good thing is that I took one look at this photo and knew exactly what the problem is. She is weaving this on a two-foot Shannock and was thinking that this was caused by a warp tension problem so she tried to improve the tension on the left side of the piece. I can't feel the tension so I don't know if it is even, but that isn't the problem in this case.

The problem is WEFT tension, not warp tension. It is true that if you have a section of warp that is looser, you'll get a bubbling up of the weft. But that isn't what is happening here. One of the most important things in tapestry is to get the right amount of weft into your warp, and that is something that an experienced weaver learns to adjust constantly and mostly without thought.

Look at the warp spacing in the photo. The warps on the left where the fell line is rising are very close together compared to the rest of the piece. When warps get close together like this, there isn't anywhere for the weft to go because the space becomes so small, so it pushes up. Often people try putting less and less weft in in this case to try to fix the problem and that is the opposite of what has to happen. This piece is effectively now being woven eccentrically on the left side which only exacerbates the problem as you need even MORE weft in eccentric weaving to maintain warp spacing.

Consider what happens with the wefts in cross section:

In this diagram, the warp threads in cross section are shown with the large black circles. Each weft thread has to have enough slack to travel over and under each of those warp threads. The warp is under a lot of tension and when you don't put enough weft in to travel the extra distance, the only option is for the warp threads to move closer together.

When your warps start to get too close together, you need to put more weft in. Said another way, when your warps get crowded together, you need to increase the bubbling in that section. Make those bubbles bigger, not smaller. The extra weft you put in will start to push the warps apart and you won't have this problem of the rising fell line. (Notice that she is also having difficulty even covering the warp with the weft and has had to pack the left side of the piece very hard to keep the warp covered. This is a situation where you'll often see lice.)

Conversely, if you have areas where your warps are spreading apart, you need to put less weft in. Often in areas where there is a lot going on, the warps start to spread out. I will flatten my bubble or use no bubble at all to encourage the warps to come back together in this case. I also sew my slits as I go to help avoid this spreading warp problem.

Weft tension, or the amount of weft put into the warp with each pick, is something that has to be constantly adjusted. Watch those warps as you weave and then check to make sure your warp tension is even. If it is, you need to watch the amount of weft you're putting in carefully. You can change the areas in one pick that get more or less weft. Areas of warp spread can get much less weft (straight line), areas of warp crowding can get much more weft (bigger bubbles which increases amount of weft).

Here is a video that shows this bubbling problem.

The entire video is part of my new online tapestry techniques class. Visit www.rebeccamezoff.com/online-learning/ for more information. Part 3 of the class has a whole module on weft tension.

This student's piece was an extreme case where I advocated unweaving or filling in the low areas and then aggressively working to get those warps on the left to move apart. Do you have other ideas of how to fix this problem? Please leave your thoughts in the comments section below if you do!

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  1. Wow, I had just about the same problem with the warps insisting on being too close on the far left.. but instead of the fell line rising, the threads were just a lot closer in that general area... although I tried to widen the area on that side, it wouldn't fix itself... I THOUGHT I was allowing more weft in on that side... I guess not! It's off the loom now, we'll see what weirdness my next tapestry piece brings!

    I decided to just keep weaving and embrace the weirdness... (this is on my Rays piece, which was just cut off today.. if you look at the photo on my blog, this tightness is at the top since the piece was woven sideways)...

    By the way, I think that piece you posted of your student's work is beautiful.. love the colors! :)

  2. Weft tension! Ack! I'm glad we'll be covering this in class. Love the visuals!

  3. Thanks for posting this, Rebecca. I usually have the problem of my warp threads spreading, but this only happens when I'm weaving a weft or warp interlock. Hopefully, you'll be covering this during one of the on line classes.

    1. We definitely will! Parts 2 and 3 are full of this kind of information. It can be difficult to avoid the spread with a weft interlock, especially if it is a long one, but there are some tricks we can use.

    2. Thank you Rebecca. I happen to really like the weft interlock so I'm looking forward to learning more on how to keep my warps straight.

  4. Presuming this piece (which is beautiful in regard to colorway!!) is a workshop sampler that will be kept for reference regarding things studied in the class, if it were mine I'd choose to leave what's there alone, and opt for learning your technique for correcting going forward (the filling in the dip and then agressively spreading the too-close warps). That way, this piece can serve as a wonderful reminder of the problem and it solutions... if the final piece were perfect, one might forget what was learnt along the way.

    1. This is not actually a workshop sampler (I NEVER would have let a student go this long with this problem), but something this student wove at home. Unweaving 18 inches seemed too painful, so she did fill in the dip and then move forward as you suggest. And yes, mistakes can be a great learning tool! (Perhaps the best learning tool possible.)


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