Lets talk mordants

In general, dyes need a little help in adhering to fabric.  I typically dye cellulose based textiles (ie. hemp, cotton, and linen) with fiber reactive dyes.  This type of dye needs soda ash (sodium carbonate) to "fix" the dyes, making them bond to the fabric fiber.  For protein fibers like animal fibers and silk, acid dyes are usually used and fixed with citric acid or vinegar.

With dyes obtained from plant material, you need a mordant.  Mordants are metal based salts that assist in dye adhesion and color saturation.  Here's where natural dyeing can get a little less eco-friendly.  Some of the metals that can be used as mordants can be dangerous and, in large quantities, can have a negative environmental impact.  Tin and chromium being among these.   Indigo does not need a mordant but we'll get to that a little later.

I chose to use alum and iron.  Both are readily available and have little environmental impact.  I purchased alum through the bulk section of my local health food store.  It can also be obtained through Dharma Trading or Pro-Chemical.  In addition to alum, I am also using an old cast iron sauce pan to simmer my dyebath.  Iron is a great mordant for muting colors with a gray cast. 

I thought it would be best to have a standard mordant formula for my experiment.  Through the many books I've read on natural dyeing, each one has a different idea for the concentration of mordant to pounds of fiber to be dyed.   I decided to do 15% wog (weight of goods) and see what happens.

For my first batch of materials:
10  2.5"x2.5" squares of hemp/organic cotton fabric
a fist full wad of Patons Classic 100% wool yarn

This batch of materials was really light so I only needed 1.15 grams of alum (approx. 1 tsp).  I dissolved it in my little stainless steel sauce pan with 20oz of water.  Then simmered the alum water with the fabric and yarn for 1 hour then let it cool.  I hung the yarn and hemp squares on the line to dry.

Now I have pre-mordanted material for when I'm ready to dye!