From the Profitable Book's "How to make your Bran Water". For use with Madder dyeing. The Whole Art of Dyeing also describes making bran water, as does the Plictho.
4.5 gal water
1 lb bran
Simmer water 15 minutes, pour into pot over bran
Stir every 2 hours for 24 hours (while awake)
let sit for four days.
First day: no change. 2nd day: bit more stinky, mucousy bits floating on top. 3rd day: definitely stinky. 4th day: smells like vomit. Ready to go!
This was redacted from the following recipe in the Profitable Book:
From experiments with madder dyeing, bran water (although slightly acidic) adds a bluer cast to madder red dyes. In addition, it softens the harsh feeling given to wool by madder. Use of bran to soften water for madder dyeing is discussed at length in James Haigh.s Dyer.s Assistant (1796). Haigh also says that bran can be used to counteract water with a high alkaline/chalk/mineral content when dyeing, by throwing a large bag of bran into the vat and boiling it for a while.
Experiments with soaking wool for long periods of time in fermented bran water (in the middle east, this technique is used when dyeing yarn for carpets) show that, when examined under an electron microscope, the sticky substance between the wool scales is eaten away, allowing deeper penetration of the dye stuffs. This results in brighter colors with much better resistance to sunbleaching.