The instructions are easy and clear - you put the dye into the drum of the front loader, cover it with 500g salt (500g no matter how much dye) and add in the damp sheets, then start a 40 degree cotton wash.
Once that's done you then put the sheets through another cotton wash to remove any excess dye (this time with detergent), and then dry them away from sunlight or direct heat. While they're drying you run the machine through an empty load with detergent. The dye is powder which surprised me, for some reason i had imagined it to be a thick liquid, but that would just be adding unnecessary weight.
The dye mixed very quickly, these two shots were taken within minutes of the wash cycle starting.
And the finished sheets! They are a wee bit blotchy in places, especially the pillowcase on top. I suspect this is due to them being old sheets with probably hidden stains from hair products, body oils etc that doesn't come out with repeated washes, but all in all it's a marked improvement on their appearance. The fading from the sun is no longer obvious, although i'll need to try to dry them out of the sun in summer to keep it like that.