Rigid-Heddle vs Two-Shaft
Is there a difference between a rigid-heddle loom and a two-shaft loom in what they can do as far as patterns, etc., go?
There are some differences, though not all are related to the pattern potential of the looms, except indirectly. On a rigid-heddle loom, you are limited as to sett; that is, your rigid heddle allows either 8, 10, or 12 threads per inch depending on the heddle. The threads are therefore usually fairly thick or far apart compared to the options possible with a shaft loom (no limits).
But with a rigid-heddle loom, you can do some types of pick-up patterning more easily than you can on a two-shaft loom. Selecting slot threads on a pick-up stick behind the heddle and leaving it in place as you weave is not possible with threads constrained in the heddle eyes of a shaft loom (see The Weaver's Idea Book by Jane Patrick for more about this). Lace weaves are especially easy to do on a rigid-heddle loom with pick-up.
Both looms mostly weave plain weave, though. A two-shaft floor loom will do this more quickly and easily than a rigid-heddle loom, allowing a pleasing rhythm. A floor loom will also allow a longer warp and a denser beat.