Forgive me for this very late reply! The Diastatic Malt Powder has enzymes in it that begin to digest the pectins and waxes in the cellulose fiber. It's essentially helping remove a tough layer on the fabric so that the mordant can better bond with the fiber, and the the dye.

That book is awesome and I continue to learn a lot from it! If you do not have aluminum acetate, you can use what's coined as Alum (aka Potassium Aluminum Sulfate), it's just known to produce stronger mordant for protein (animal) fibers. That book says "when combined with soda ash solution, alum becomes a mordant for cellulose." But I've never tried it. Hope that helps! Dyes that are tannin rich can also dye fibers without any mordant needed. The tannins act as a binder between the dye and the fiber

Forgive my for this very late reply. If it is a cotton dress, I would recommend the method in the video above. You could also add a l layer of tannin to this recipe (ex: making an oak gall pot and soaking the fibers in it for about 30 min.) . Alum mordants are relatively non-toxic to the environment. It is best to dispose of them down the drain though, rather than in the garden. If you'd like to omit using Alum, than your best option is to scour the fabric and add a tannin layer. Best of luck!

This process is intended for plant fibers. Other natural fibers that are animal fibers need a lot less steps in preparation for dyeing

hey! You will want to rinse under running water. Then you can immediately dye with this wet fabric, or let it dry and store away for future dyeing.