1st Inaugural Indigo Apprenticeship Blog Entry #3 by Amanda Gough

From Sludge to Shelf: Filtering , Muslin-Filtering, and Dehydrating Indigo Pigment

This Blog has several pieces written by Amanda Gough, AFA and Indigo Shade Map Intern & Apprentice

Before you start: how to know the pigment is ready to filter

• Distinct layers: A clear or tea-tinted liquid on top and a darker, inky sludge at the bottom.

• Time settled: Typically a few days  after aeration process.

Step 1 : After the Aeration process Let the pigment settle completely

1. Place your extraction vessel somewhere it won’t be bumped.

2. Cover loosely to keep dust out.

3. Give it enough time to form a crisp boundary between clear liquid and pigment. If the line is cloudy, wait longer.

Tip: Cooler temperatures and stillness improve settling.

Step 2 :  Remove the clear liquid

Goal: Remove as much supernatant as possible without disturbing the pigment.

We used pitchers

Stop when the liquid begins to look milky/colored—this means you’re nearing the pigment layer.

Rosa Chang Korean Indigo Master displaying properly processed liquid being removed from the container. Image by Amanda Gough, AFA

Step 3 : Consolidate the pigment

1. If you have multiple containers, combine the sludge into one vessel.

Upcycled Muslin with Indigo Print after filtration process. Photo by Amanda Gough

Step 4 : Set up your muslin filter

1. Stretch 2–3 layers of muslin over a clean bowl/strainer or hoop.

2. Secure with clamps or rubber bands so the cloth won’t sag or collapse.

Apprentice Timothy Prieto Scraping the fabric to assign the filtration process. Photo by: Amanda Gough

Step 5 :  Filter the pigment through muslin

1. Pour the pigment sludge slowly into the center of the muslin.

2. Let gravity work until dripping slows.

3. Draw the muslin corners together to make a bag and gently twist/squeeze to press out more water.

4. If the cloth clogs, pause, scrape the surface with a spatula to expose clean weave, or transfer to fresh cloth.

Result: You’ll have a dense indigo paste inside the muslin and relatively clear filtrate in the bowl.

Step 6 :  Prepare dehydrator trays

1. Line trays with silicone dehydrator sheets or parchment so the paste won’t bond to the mesh.

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Step 7 :  Spread the paste

1. Transfer paste from the muslin to the lined trays.

2. Use a spatula to spread it into thin, even sheets

3. Label the tray (batch/date/process notes).

Step 8 :  Dehydrate low and slow

1. Turn on the dehydrator

• Cooler settings preserve color and reduce “baked” binder smells if any organics remain.

2. Dry 6–12 hours, checking every couple of hours. Time varies with thickness and humidity.

3. Dryness test: The sheet should be crisp and snap cleanly; no cool or tacky spots.

No dehydrator? Air-dry on lined trays in a dust-free space 1–3 days. Avoid direct sun and drafts that might blow pigment away.

Indigo Master Rosa Chang and Apprentice- Intern Amanda Gough participating in the filtration process. Instax by Timothy Prieto

Step 10 :  Break, grind, and store

1. Lift the sheet; it should peel from the liner.

2. Break into flakes. If desired, use a mortar/pestle to make a fine powder (wear a dust mask).

3. Store in airtight glass jars or mylar bags. Add a food-safe desiccant if humidity is high.

4. Label with: plant/species, date, method (fresh-leaf/lime %, washes), and any notes.