The Zigzag beading technique combines two sizes of
round beads set on flexible beading wire that travels through the base
Byzantine chain. This embellishment is available
in a variety of color choices of combining, 6mm amethyst with 3mm quartz,
or both bead sizes in royal-blue lapis lazuli, or black onyx set on
flexible beading wire and secured with crimp beads.
I have a tutorial online at PBS's beads, baubles, and jewels.