Dye Project: Logwood Exhaust 2 (Alum + Iron)

For this dye project, we’re dyeing cotton, linen, and wool with logwood. Two years ago, we dyed with logwood chips, and produced a rich purple color (see Dye Project: Logwood). I saved the dye, so this will be the second extract.This time I plan to split the project into two dye baths – one for fabric treated with an alum brightener and the other with a ferrous sulfate (or iron) brightener. Iron darkens (or “saddens”) color.

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 help keep the dye bath at a consistent temperature. You also need:

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

NOTE: For safety, wear rubber gloves and a face mask. Logwood comes with strong warnings that it can cause serious skin, eye, or respiratory irritation, and soda ash is caustic.

Basic equipment

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

• Cotton dish towel (cellulose)
• Cotton tee-shirt - alum only
• Cotton fabric
• Cotton napkins
• Linen coasters (protein)
• Linen fabric
• Wool yarn

Fabric for alum brightener

Fabric for iron brightener

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

• For the alum and soda ash brighter, the WOF is 11.5 ounces (326 grams):
• 15% Alum = 49 grams (3 Tablespoons)
• 2% Soda ash = 6.5 grams (1.3 teaspoon)
• For the iron and soda ash brightener, the WOF is 7.8 ounces (221 grams):
• 2% Iron sulfate = 4.42 grams (1 teaspoon)
• 2% Soda ash = 4.42 grams (1 teaspoon)

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 dye bath.
4. Rinse and hang to dry.

Pour the logwood dye into the dye pan. I’m using a half gallon of Extract 2 for each batch. Agitate the jar to mix any sediment that has settled to the bottom of the jar. Note that after two years, the dye appears brown. I wonder if any purple pigment remains! Add enough water to cover the fabric. Logwood dyes best in hard water, so I’m also adding a single antacid tablet to each batch. Bring the dye bath to a simmer.

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. Simmer the fabric 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 fabric 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 in dye overnight.

Squeeze out fabric (alum)

Squeeze out fabric (iron)

Squeeze out excess dye from the dish towels. 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 two dye batches. Let the towels air dry. In a couple of weeks, run the towels 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 a pale lavender. For the iron brightened batch, the color is a darker shade of lavender (described as "saddened"). The color also differs slightly between fabric types. Unfortunately, the color distinction does not photograph well, but it is detectable in certain light.

Subtle color shades between logwood Extract 2, and alum and iron brighteners

Logwood is not considered lightfast, and fades over time. Iron can be used to mitigate fading, so it will be interesting to compare the alum and iron-based colors over time. Keep in mind that our dye is two years old, so time may have influenced the outcome. I’m pleased with the subtle color results from Extract 2, and it’s fascinating to see the range of colors produced across fiber types, even when basic variables are the same. Still, I’ve decided not to save the dye bath for a third extract.