Hi Wayne:
I'm the one who used the phrase "big arc or rainbow line". When you finish
weaving a row, you shape the yarn into a curve before packing it down. The
children relate to the rainbow description because they all seem to know
what one looks like.
There's probably a good book or website on elementary weaving that would
show you a picture of this. If you ever come to NJ I'll show you all my
weaving tricks.
Sky