My plan was to mordant with a vinegar solution. Then I saw in one of my old books that linen is supposed to be scoured and bleached with "alkaline lye" before mordanting. Of course, I can't find the recipe I was going to use now when I want it, so I'm poking around in my books. (sigh)
I can't seem to buy lye here as all the hardware stores seem to think I will make nefarious and illegal things in my bathtub with it. (?) Apparently this has been a major problem and it has stopped any lye soap-making in these parts unless one has a business license specifying purchase of a certain class of chemicals. Very frustrating. I have not tried to import it either, but I wonder if I need the lye at all if the linen was purchased white. I already washed out the sizing.
If anyone has links for how to dye with beet "juice" I would love them. Also would enjoy knowing of your experiences with beets. Thanks for taking the time.