How to Mordant Cotton Fabric

Learn the exact steps of correctly mordanting any cellulose fabrics with Aluminum Acetate before eco printing or natural dyeing

Preparing your cotton fabric with the correct mordant before dyeing is key to achieving light-fast and long-lasting colors, when you dye your cloth with natural plant materials.

Have you ever dyed a piece of cotton fabric with a plant dye only to have the color disappear as soon as you rinse it with water? What the heck happened?

Chances are that you did not apply a mordant to your fabric prior to dyeing it.

Plants, minerals, mushrooms and other natural materials have been used to create a rainbow of colorful fabrics for thousands of years but they do need a bit of special preparation to get the color to “stick”.

What is a Mordant?

In a nutshell, a mordant is a substance that acts as a binder which lets your dye particles adhere to your fabric.

The fabric itself cannot hold onto the dyes. Mordants form a bridge between the dye and the fabric, creating a bond that can help to make your fabric more colorfast and washfast.

Common mordants include alum, iron, and soy milk each adding its own twist to the final color outcome. (i.e. iron darkens or ‘saddens’ your final color).

NOTE: Some heavy metal mordants, such as tin can be highly toxic to work with and require special handling considerations.

Not all mordants work with all fabric types. For instance, if you are planning to dye protein (animal) fibers such as wool or silk, you would like mordant with Potassium Aluminum Sulphate (PAS), commonly referred to as Alum. For cellulose fibers such as cotton or linen, you would use Aluminum Acetate (AA).

After many years of experimenting with a variety of mordants, I now prefer to work mainly with Aluminum Acetate or Soy Milk for cellulose fibers and Potassium Aluminum Sulphate for protein based fabrics.

Mordanting Cotton and other Cellulose Fibers

As I said above, Aluminum Acetate is a great choice for cellulose fibers like cotton. It is very easy to use and fairly easy to find.

Step-by-Step Mordanting Process

Step 1: Scour Your Fabric

Before you begin mordanting your fabric, it is super important to make sure it is completely clean. Any oils, stains, or other impurities can keep your mordant from adhering properly, giving you an uneven result.

Note: Brand new fabrics also need to be scoured to remove any sizing or leftover detergent.

This article will teach you step by step how to properly scour your cellulose fabric.

Step 2: Prepare the Mordant

Before you can make your mordant solution, you have to do a little math. As a general rule of thumb, you need about 5-8% weight-of-fiber (WOF) in powdered Aluminum Acetate. For example, if your fabric weighs 100 grams, use 5 to 8 grams of AA.

1. Weigh your fabric with the postal scale and calculate the amount of AA needed.
   (If you do not have a postal scale …. according to Printful.com, a medium-sized t-shirt made from a standard cotton fabric weighs around 4.5 to 5.5 ounces (roughly 130–155 grams)”
   
2. Measure the AA powder and dissolve it in hot water (remember to wear your dust mask)
3. Fill the large pot or bucket with very warm water to cover your fabric and then add the dissolved aluminum acetate. Stir to incorporate.

How to Mordant Cotton Fabric with Aluminum Acetate for Eco Printing and Natural Dyeing