Dye Project: Cochineal Exhaust 2 (Alum + Iron)

For this project, we’re dyeing cotton, linen, and wool with cochineal. Cochineal is light- and washfast and produces a broad range of fuchsias, reds, and purples. Two years ago, we dyed with cochineal and produced a rich fuchsia color (see Dye Project: Cochineal (Bugs!). I saved the dye, so this will be the second exhaust. We’ll use two dye baths – one for fabric that has been treated with alum and the other with Ferrous sulfate (or iron, which darkens or "saddens" color). 

Note that I sometimes use "exhaust" and "extract" interchangeably, to mean the number of times the dye has been used. The first time the dye is used is Exhaust 1, and the second time is Exhaust 2. I prefer to use "exhaust", and reserve the use of "extract" to mean the number of times dye is extracted from the source (I extracted dye six times from the same batch of cochineal insects two years ago). Also note that I recorded various pH values throughout the dye process. I'm not sure what to do with the information yet, but thought it would be useful to start collecting it.

For this project you need basic dye equipment, and a well-ventilated workspace. You need a soaking pot, a dye pot, a heat source, and a candy thermometer to maintain the dye bath at a consistent temperature. You’ll also need:

• Prepared dye (Exhaust 2)
• A gallon or two of distilled water (plus more as needed)
• Prepared fabric (scoured, gallnut mordant, and alum or iron brightener with soda ash fixer)

NOTE: For safety, wear rubber gloves and a face mask.

Basic equipment

For each batch, we are dyeing both cellulose and protein fiber:

• Cotton dish towels (cellulose)
• Cotton fabric
• Cotton napkins
• Cotton handkerchiefs
• Linen coasters (protein)
• Linen fabric
• Wool yarn

Protein and cellulose fabric and fiber for dyeing

The Weight of Fabric (WOF) is used to calculate the mordant brightener proportions.

• For the alum and soda ash brightener, the WOF is 8.7 ounces (248 grams): 
• 15% Alum = 37.2 grams (2.5 tablespoons)
• 2% Soda ash = 5 grams (1.13 teaspoon)
• For the iron and soda ash brightener, the WOF is 8.7 ounces (247 grams):
• 2-4% Iron sulfate = 5-10 grams (1-2 teaspoon; I used one rounded teaspoon)
• 2% Soda ash = 5 grams (1.13 teaspoon)

Per Maiwa, adding iron shifts the color towards purple, and adding alkaline, like soda ash, shifts the color toward deep fuchsia.

Dye the Fabric

The basic dye process:

1. Bring dye bath to a simmer.
2. Add wet fabric and simmer for an hour.
3. Allow to cool in the dye bath.
4. Rinse and hang to dry.

First, I combined all my stored jars of cochineal Exhaust 2 from two years ago. I stirred and agitated to incorporate the sediment that had settled at the bottom of the jars. After two years, the dye was still a deep glossy fuchsia. A couple of the storage jars had a strong, rather unpleasant odor, but no deterioration of color.

Combined cochineal dye for Exhaust 2

Pour the cochineal dye into the pan. I’m using half a gallon of Exhaust 2 for each half-pound batch, and enough water to cover the fabric. Maiwa recommends using distilled water, which is pH neutral. Out of curiosity I tested the distilled water and our tap water. The pH for each is 6, so distilled water may not be needed here in the Bay Area. Maiwa also informs that cochineal is pH sensitive, and you can shift the dye color by adding acid (vinegar) or an alkaline (soda ash). See the Maiwa Guide To Natural Dyes for more information. In this project, I'm using alum and iron mordant brighteners to influence the pH of the dye bath, and the color of the fabric.

Dye bath (fabric treated with alum brightener)

Dye bath (fabric treated with iron brightener)

Add the presoaked, prepared fabric to the dye bath, without rinsing. Stir to loosen the fabric. Add water to cover. Bring the dye bath to a simmer, over the course of an hour. Then simmer the fiber for an hour, keeping the temperature between 170-180º F (77-83º C). Continue to stir periodically for even dyeing, turning the fabric frequently while simmering. Turn off the heat and let the pan cool, leaving the fiber in the dye bath.

Soak fabric in dye overnight (alum)

Soak fabric in dye overnight (iron)

I transferred the project to a bucket, and started the second batch. To capture as much color as possible, I soaked both batches overnight.

Squeeze out fabric (alum)

Squeeze out fabric (iron)

Squeeze out excess dye from the fabric (but save the dye bath for a third exhaust)! Rinse the fabric in cool water until the water runs clear. Run the fabric through the washing machines' rinse and spin cycles without soap. I ran them separately, to keep track of the dye batches. Let the fabric air dry. In a couple of weeks, run the fabric through the washing machine using Synthrapol or Professional Textile Detergent, and rinse. Air dry again.

Hang to dry (alum)

Hang to dry (iron)

For the alum brightened batch, the color is lovely pink. For the iron brightened batch, the color is a deeper lavender (and reminds me of the shades produced from logwood Exhaust 2). The color also differs between fabric types. As with logwood, the color distinction does not photograph well (at least with my setup), but it is more distinctive in person.

Color differences between cochineal Exhaust 2, and alum and iron brighteners

In summary, the fabric color that was produced by Exhaust 1 two years ago has faded, even though the fabric was stored away from the light. The color from Exhaust 2 is less intense than the original Exhaust 1, but that is as expected. The dye becomes lighter with each exhaust (plus, the dye is two years old). Following is a summary of pH values recorded through the process (as mentioned above, I'm not sure what I'll do with the information yet)!

• Alum/soda ash mordant bath: the pH is 3.
• Iron/soda ash mordant bath: the pH is 9.
• Combined cochineal dye: the pH is 7.
• Distilled water: the pH is 6.
• Our tap water: the pH is 6.
• Combined dye bath, distilled water, and alum mordant: the pH is 5.
• Combined dye bath, distilled water, and iron mordant: the pH is 9.

Cochineal Exhaust 3 for a future project!

I’m pleased with the color results from Cochineal Exhaust 2, and it’s fascinating to see the range of colors produced across fiber types, even when basic variables are the same. I am preserving the dye in a glass jar to use again, and marking it as Exhaust 3. The dye color may be less intense, but is still usable, either for a lighter shade or mixed with another color. As always, there are more opportunities ahead to experiment!

Color Comparison

For fun, look at the range of shades produced with cochineal dye, over two exhausts, and using alum and iron as mordant brighteners!

Cochineal:  shades of color produced