I love the look of rickrack...very retro....like using piping....sometimes it is the only thing that works.....
if you have old-old-old rickrack it could be cotton, I would suggest washing, perhaps just in a bathroom sink in
hottest water, I personally prefer to follow the zig zag when sewing so it lays nice and flat....but that is a personal choice, some like the little teeth flapping in the wind......