The shawl itself is simple: neck down triangle that grows twice at fast at the edges as it does in the middle, knit in loose stockinette.

However, it uses a technique called Navajo Ply Knitting (or chain knitting) for 4 rows and single strand for 4 rows. Alternating the two accentuates the delicate fineness of the lace yarn and makes very subtle stripes.
NAVAJO PLY KNITTING
This technique makes one strand of yarn into three strands without cutting the yarn or estimating quantities of yarn left. Also see video at: https://zombieyarns.com/blogs/lorna-dyes-again.