One of the things I love about my rigid heddle loom is its simplicity. Its primary strength is its ability to make beautiful plain-weave cloth rapidly and easily. Plain, or tabby weave, is when a weft yarn crosses over one warp yarn, under one warp yarn, across the width of the fabric, just as you would do to make a lattice pie crust. If you like to create visual interest in handwovens by varying the order of colors and textures of yarn, and complete a project in less than a day, you can hardly do better than to warp and weave on a rigid heddle loom.
I weave with double heddles for a double-density sett with finer yarns on my loom, but I still am weaving plain weave. Both heddles go up for one shed, both heddles go down for the other shed. But after producing dozens of plain-weave scarves, table runners, pillow covers, etc., the thought comes creeping: “What other structures might I be able to create on this loom?”
My library of weaving books and videos is full of advice on how to make a rigid heddle loom act like a 4-shaft loom, but the process always seems so complicated! Weave with 3 heddles, or use multiple pick-up sticks, or add heddle rods. If I want to do a complicated weave structure, I have floor looms for that. I want an alternate weave structure I can create with just the two heddles I already use.
After poking around on the internet, I found an answer: twill weave, but specifically 2/1 twill. The salient feature of twill is its pronounced diagonal lines created by small floats of yarn crossing over two or three yarns in the web. Having first learned to weave on floor looms with a number of shafts that are multiples of 4, I tend to think of twill as a balanced 2/2 twill or an uneven 3/1 – 1/3 twill. A 2/2 twill means a weft thread goes over two warp yarns, under two warp yarns, with each new row offset by one warp thread. A 2/2 twill looks the same on both sides of the fabric and the diagonal lines form a 45° angle.
Denim, used for blue jeans, is typically woven in a 3/1 twill, whereby a weft thread crosses over 3 warp threads, under one warp thread on one side of the fabric. The other side of the fabric is a 1/3 twill, with the weft crossing under 3 warp threads, over one warp thread. Denim is made with indigo-dyed warp and white weft, so the two sides of the fabric look different. The “right” side shows more indigo warp floats, the “wrong” side shows more white weft floats, and the diagonal lines frequently form a 30° angle.
“Right” side of denim 
“Wrong” side of denim
Now, back to the 2/1 twill that can be woven on the rigid heddle loom with only two heddles and no pick-up sticks or heddle rods. With the help of my internet sources and some mental gymnastics performed during wakeful hours late at night, I realized I could thread the loom at 1.5 times the density of a single heddle in a 2/1 threading. One third of the warp threads go through the holes of one heddle, another third go through the holes of the second heddle, and the final third of warp threads go through the slots of both heddles. Any shed made with this threading is always 2 against one – plain weave is not possible with this threading.
This picture shows the three groups of warp threads. Top layer goes through holes in back heddle, slots in front heddle. Middle layer is threads in slots on both heddles. Lower layer is threads in slots on back heddle, holes in front heddle. Each shed is made by opening one layer away from the other two.
This 2/1 twill is woven in a 3-heddle sequence: 1) one heddle up, the other in neutral, 2) the second heddle up, the first in neutral, 3) both heddles down, making the loom act like a 3-shaft loom. This fabric is weft-dominant on one side and warp dominant on the other, just like the denim fabric, but with the diagonal lines forming a 60° angle.
I wove a scarf with the weft-dominant side facing up on the loom, warp-dominant side facing down for the whole length of the project. The two sides of the fabric appear quite different from each other. Next, I wove a scarf with alternating sections of weft-dominance and warp-dominance. To achieve the alternating pattern, I modified the 3-heddle sequence to 1) one heddle down, the other in neutral, 2) the second heddle down, the first in neutral, 3) both heddles up. I also reversed the sequence to get a zig-zag pattern of diagonal lines.
This scarf is weft-dominant on one side (left), warp dominant on the other (right). 
This scarf has alternating sections of warp dominance (gold) and weft dominance (teal).
The scarves pictured above were woven with a straight twill threading, i.e., 1-2-3-1-2-3. I wanted to see if I could thread the warp in a point twill: 1-2-3-2-1. The answer is Yes! I wove the scarf below with one 3-heddle sequence to achieve a pattern of diamonds on the weft-dominant side (blue) and another sequence at the opposite end of the scarf which created little elongated ovals on the warp-dominant side (red).
The lesson learned is that the versatile rigid heddle loom can do more than one simple weave structure. Let’s hear it for twill!
I Dyed it My Way 