As I dicussed in my post about what looms do, most looms have “shafts” that allow you to lift a specific set of warp threads when you need to.
The rigid heddle loom is a bit of a special case, because it acts as a 2 shaft loom, even though all it’s heddles are all linked together. How does it achieve this? Well, by having a reed with “slots” and “holes” as you can see in the pic below.
When you raise the reed into an “up-shed”, the threads in the holes get lifted up to form the top of the shed. When you lower the read into the “down-shed” position, you pull the threads in the holes down to form the bottom of the shed.
The threads in the slots don’t really move – the slot allows the reed to move around them as it is lifted or lowered.
This allows you to do some fun patterns using plain weave and techniques where you manually manipulate different threads.
There’ll be a lot more to come on this!
One thing to keep in mind when looking at colour patterns for 2 shaft looms, is that not all of them will conform to a neat slot/hole/slot/hole pattern. It’s easier to explain this if you think of your slots as “shaft 1” and the holes as “shaft 2”.
In some cases, a pattern might require you to thread the reed:
shaft 1/shaft 1/shaft 2/shaft 1/shaft 1/shaft 2
You can do this with a rigid heddle, but it’s important to keep in mind that the reed partly determines the spacing of your warp threads, so if you start bunching too many threads into a single slot, you might hit a problem.
The alternative is to spread the threads over multiple slots, but skip the holes between them – again, assuming this doesn’t mess with your warp spacing (sett) too much. Skills to learn!