Scouring Cotton & Linen for Natural Dye

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Before you can achieve beautiful natural color on plant-based fibers, you need to deep clean. In this post, I’ll walk you through how to easily scour cotton and other plant based fabrics.

yarrow, soda ash, a pot of white fabric, and a wooden spoon on top of a wooden cutting board.

When you first start researching natural dyes, it’s exciting! You want to dive right in and reveal the beautiful colors nature has to offer. But before you begin, it’s important to remove anything on your fabric that might repel or block those colors from taking hold.

Scouring is the first step I took when I dyed with dandelions, and pecan hulls. When I pulled my fabric out from the dye pot I knew I set myself up for success with this essential first step.

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What is Scouring and Why it Matters
Supplies You'll Need
Step-by-Step: How to Scour Cotton and Other Plant Fibers For Natural Dye
Dyers Tips
FAQ
Related

What is Scouring and Why it Matters

Scouring is the process of deeply cleaning fabric. Industrial processing of fabrics often contain chemical residues along with dirt and grease. Cotton, linen, and other plant based fibers also contain natural oils which can hinder the dying process.

When we remove these residues, natural or not, it will help ensure we get the most even uptake of the mordant we use next, and then ultimately the natural dye.

Supplies You'll Need

I recommend using dedicated equipment for all your dyeing projects—especially for mordanting and dyeing steps down the line. (The food scale is the only exception if you want to keep it for kitchen use.)

Plant-based fiber – Any undyed cellulose fabric you want to scour and dye (like cotton, linen, or hemp). For this post, I’m using 100% cotton flour sack towels, which I plan to cut into smaller pieces for swatching and testing natural dye colors.
Large Stainless Steel Stock Pot
Wooden Stir Stick
Soda Ash - also called washing soda or sodium carbonate.
Food Scale - (optional but recommended especially for future step in separate posts)
Small spoon - used for measuring powders
Scratch paper & pen - for taking notes and recording WOF (weight of fabric).

Step-by-Step: How to Scour Cotton and Other Plant Fibers For Natural Dye

Follow these essential steps to properly scour cotton, linen, or other plant-based fabrics. Use the printable card below to keep the process on hand for next time!

white cotton fabric being weighted on food scale next to scratch paper.

Step 1: Weigh & Pre-Soak
Weigh your dry fabric to calculate your WOF (Weight of Fabric). I like to weigh in grams.
Pre-wet your fabric in water for 30 minutes.

Soda ash being measured out on a black food scale.

Step 2: Mix Your Soda Ash Solution
Calculate soda ash at 2% of WOF:
WOF × 0.02 = weight of soda ash
Example: 228g × 0.02 = 4.5g soda ash
Dissolve the soda ash in hot water separately.

No scale? Use 1 teaspoon soda ash per gallon of water to get the job done.

Pouring scouring liquid in silver pot with a white cotton textile.

Step 3: Simmer the Fabric
Add the soda ash solution to the pot with your fabric. Make sure there's enough water so the fabric can move freely.
Bring to a boil, then reduce to a simmer for 1–2 hours, stirring occasionally.
You may notice the water turning brown or yellow—this is normal!

Scouring cotton fabric in silver pot and stirred by wooded spoon.

Step 4: Cool, Rinse, & Repeat if Needed
Let the fabric cool, then rinse thoroughly. Repeat once more if fabric still feels dirty, or move on to mordanting.
You may also hang to dry and store to mordant at a later time.

Dyers Tips

Pre-wetting your fabric helps the scour bath penetrate evenly. I know it seems unnecessary but remember we are setting ourselves up for success!
Add enough water to the pot that allows the fabric to easily move around. From my experience, there is no hard and fast rule for how much water to add other than this.
If you are storing your dried scoured fabric and mordanting at a later date, remember to throughly dry, store (I use zip-lock bags) and label with today's date, fabric type, and WOF.

FAQ

Does soda ash produce suds?

No. Soda ash does not produce bubbles like soap or detergent, so don't worry it's doing its job!

Is washing soda the same as soda ash?

Yes! Washing soda is soda ash — both are different names for sodium carbonate. Just make sure the packaging says 100% sodium carbonate with no added ingredients or fragrances.

Can I use this process with protein fibers like wool or silk?

Nope! You'll be seriously disappointed if you try (it would ruin your fabric).
There is a completely different process for protein fibers. Right now, I only work with plant fibers, but if that ever changes I will be sure to make a post.

Do I need to scour fabric that’s already been washed or is secondhand?

Not everyone agrees, but I think you should. Thrifted textiles or old shirts that have been washed many times can still hold onto fabric softeners, detergents, or body oils!

Can I add soap to the scour bath?

Some people do! Soda ash works great on its own, but it’s common to add a small amount of grease cutting soap for suds.
Plain Dawn is often recommended because it’s super accessible and works great. If you use Dawn, just add a tiny bit—about a ¼ teaspoon or less per gallon of water—so you don’t create too many suds.
Also, be sure to follow any instructions if you’re using specially made cellulose scour detergents along with soda ash.

Check out some of my dying projects: