The extra holes in some of the tablets (maybe 1/4 of the tablets overall? Sadly I didn't count them - my time was very limited) didn't seem to be used in this piece of weaving - my guess is that those tablets were sometimes used for a different purpose, though what that might have been I don't know. Perhaps they could be used for making cords or else for some sort of automated brocading? Most mysterious.
Yes, and sounds like fun to experiment with. It's certainly being put on my List Of Things To Try!
Thanks very much for the other answers Shelagh, it gives food for thought. I haven't tried soumak yet either so this is all very interesting!
Gina Barrett Leicestershire, England
