Saran wrap is birefringent. Turns out.
... but shiny new 0% reflected polarization pellicles are not! Isn't it snazzy? That little golden circle of cellulose is the key to our depolarization measurements (and my general happiness). Colin and I managed to get it aligned (again) yesterday :) This means that our depolarization measurements (water clouds vs. ice clouds) might have a chance of telling us something useful!