An important and necessary step to dyeing with natural dyes is to prepare the fiber for the dye. My daughter and I made a video sharing our process of mordanting fabric. All mentions of "alum" refers to "potassium aluminum sulfate".
Prepare Fabric for Dye
- Weigh your fabric dry, this number is the weight of Fabric or WOF. It's helpful to keep notes, you will need to reference the WOF later when adding dye.
- Prepare your fabric by scouring/washing with very hot water and neutral detergent, like synthropal. This prewash removes sizing, dirt and grease on the fabric that would interfered with the dye bonding with the fabric. It is customary to score fabric in a large pot to thoroughly wash the fabric.
- Add alum to a pot with warm water. The amount of alum you need to add tis 15% of the WOF.
- Dissolve the alum into the warm water and stir, the alum bath is ready for fabric.Take your time, unfold and smoothly add the fabric to the alum bath. If your fabric is scrunched, bunched or folded, these creases and lines will show-up in the dye process.
- Soak your fabric overnight in the alum mordant bath, no heat is necessary just a nice long 8 hr room temp soak.
- Remove the fabric from the mordant and hang to dry on a clothes line.
- You can start dyeing right away with damp fabric, or dry the fabric to use whenever you are ready to dye.
- If saving fabric with mordant applied to it, it's helpful to label, because it's an invisible step it's easy to get confused what fabric is what. Store fabric out of direct sunlight for as long as you need. If you are working with silk or wool it is not recommended to store them longterm, left too long with mordant and no dye molecule the fiber will breakdown and weaken. It's recommended to use silk and wool just days or weeks after mordanting.
Note* Mordant procedures for protein and cellulose fibers are not interchangeable, we did not soak our silk overnight, instead we soaked it for only a couple of hours. This was our shortcut, rule-bending, kid-attention-span way to mordant all of our fiber in one pot.
You can source alum from local art supply shops or online from dye supply stores, search "potassium aluminum sulfate". Also, "aluminum acetate" is another type of alum, often the prefered alum mordant for cellulose, or plant based fibers. If your solely focused on cotton, linen, and hemp, it can be worth the extra expense for aluminum acetate, it's helpful in achieving rich color results on plant based fibers.
When mordanting silk I soak in the Alum warm, for only for 1-2 hours. When mordanting wool I soak in the Alum cold, overnight or for 24 hours, along with my cellulose fibers.
Tie off skeins of yarn so they don't get tangled in the mordant and dye bath. Tie it multiple times, every hand length apart, around the skein, in a loose "8". Not too tight or the mordant and dye will not be able to penetrate the fibers evenly and you'll have light or white rings around the yarn - but hey this could be cool if your intentionally trying to achieve variegated colors with knitting or ikat design for weaving!