How to Mordant Fabric Before Natural Dyeing with Plants

Plant dyeing fabrics is a fairly straightforward process, but the part most people feel intimidated around is mordanting. Mordanting is a process of preparing your fabric to be plant dyed. It’s an essential step in creating a color that lasts longer and looks brighter than dyeing your fabric without mordanting. A mordant helps the dye bind to the fiber and have a longer lasting result. This is a bit technical, so if you're here as a beginner and want to try natural dyeing without mordanting, check out my dye kits. I have already done the mordanting for you and you can get into the fun part. Find the dye kit in my shop here. Let’s get into it!

Terms you may need to know:

• Lightfast: How well a fabric is able to retain its original color when exposed to light.
• Colorfast: A fabric’s ability to maintain its color without fading
• Washfast: How well a fabric is able to retain its original color when washed.
• Alum: A chemical compound often used for mordanting fabric.
• Scour: Deep cleaning a fabric to prepare for dyeing or mordanting.
• Weight of the Fabric (WOF): The weight of dry fabric, which is used to calculate mordant bath ratios.

examples of madder dye with no mordant in my dye journal 

What is Mordanting

If you’re saying to yourself, “what is a mordant,” no fear! We’ll cover that too. But to start, let’s dive into why mordants, and mordanting, is important.

On a high level, mordanting helps ensure your plant dyes last. This means as you wash and wear your fabric, the dye is likely to maintain its shade and vibrancy for longer — with the right aftercare, of course. Natural fading over time is normal, and is likely to happen. However, mordanting can slow that process significantly.

A mordant is the binding agent in your dyes, ensuring you achieve the color you’re looking for. Few plant dyes, like Indigo, don’t require a mordant, instead undergoing a reduction and oxidation process. Though mordanting isn’t a necessary step, it is highly encouraged to achieve the rich hues you’re looking for.

stirring cotton fabric in two large mordant baths

Choosing a Mordant

Often a mineral salt base, the pH levels of your mordant can significantly impact the tone of your color. I exclusively use non-toxic mordants, and my preference depends on the type of fiber I’m using, the color I’m trying to achieve and the type of dye I’m using. Finding the perfect combination may take experimentation, however alum, a metallic salt compound, is a great place to start.

Alum is the most common non-toxic mordant you can work with. It’s known for brightening or enhancing the color of your dye, and when mixed with different compounds to increase or decrease acidity, it can significantly change the tones of your dye.

Another factor to consider: the type of fabric you’re working with. I use alum acetate to prepare plant fibers and alum potassium sulfate to prepare animal fibers. In general, synthetic fibers, such as nylon and polyester, will not take well to plant dyes.

Please note: Plant fibers often require additional steps in the mordant process to improve colorfastness and the evenness of your dye. Often, you will need to scour your fabric in a heated bath with pH-neutral detergent and an alkali solution, like soda ash. These fibers may also benefit from a tannin bath before dyeing, however it’s not entirely necessary.

pillowcases being mordanted for a workshop

When to Mordant Your Fabric

Technically, mordants can be applied before, during or after you dye your fabrics. Some folks will add a mordant to the dye bath, or soak their pre-dyed fabrics in a mordant, but I’ve found that method can produce uneven dye patterns. When I mordant my fabrics — soak in a mordant bath before dyeing — it produces the best results. This process allows me to dye different fibers in the same bath, prepare my fabrics further in advance and ensure a more evenly-distributed dye.

Mordant Alternatives

Soy Milk: Believe it or not, soy milk can serve as a unique alternative to your standard chemical mordants. It isn’t technically a mordant since it doesn’t chemically bond with the fibers, but soy milk coats fabric with a protein “film,” helping dyes bind more effectively. It works best with plant fibers, and I’ve had the most success when paired with yellow dyes.

Tannin: Tannins are plant compounds that, when used as mordants, can help plant fibers better absorb dyes, behaving like an animal fiber. Some plant fibers don’t require tannins, however they can be used to alter the color of your fabrics and dyes. Examples of tannins I like to use are tara, pomegranate rind and chestnut.

Mordant Tips and Safety

Though I always use natural, non-toxic compounds, it’s best practice to create your mordant bath in a well-ventilated area and wear a mask and gloves. Compounds like alum can irritate the eyes and lungs, so begin with caution and adjust your process from there. If you hand mordanted fabric without gloves, it will make your hands really dry. Ask me how I know! Best to just take precautions.

To avoid cross contamination, it’s best to keep your dye supplies and kitchen supplies separate. That may mean you need to purchase a separate set of measuring cups and a new pot, but most of these materials can be found secondhand. Necessary supplies include:

• Your preferred fiber (soak in water beforehand for the best results)
• One large metal pot (for alum potassium sulfate + animal fibers)
• One large bucket or plastic bin (for alum acetate + plant fibers)
• Kitchen scale OR a measuring cup & measuring spoons
• Your preferred mordant
• Water (enough for fabric to flow freely in the pot)
• Mixing vessel + whisk

Your mordant bath ratio will depend on the weight of your fabric (WOF). Protein fibers are often recommended to use a 10-20% WOF bath, while plant fibers are recommended to use a 5-10% WOF bath. For example, if you’re dyeing a 200g wool skein and plan to prep a 20% WOF bath, you would add 40g of your preferred mordant.

I typically use about 15% WOF of alum in my work. To prep your bath, bring your pot of water to a simmer and add your mordant. Ensure they’re completely dissolved before adding damp fiber to the pot and let simmer for 1 hour, stirring occasionally. At the end of the hour, turn off the heat and let your fiber cool in the pot. Once it’s completely cool, you can hang to dry and dye later or dye immediately.

Alternatively, if you’re using a plant fiber, I add the alum into a measuring cup and dissolve it into a small amount of boiling water. Then, I add it to a large bucket filled 2/3 of the way with warm water. I add the fabric (you want to add it when it’s damp - so run it under water first) and submerge it with a large metal spoon. I let the fabric sit in the bucket overnight and remove it the next day, squeezing out all the excess liquid and then adding it into the dye bath.

Once you’re finished with your mordant bath, you can reuse it by added small amounts (about 5g) of alum with each additional piece of fabric added. After a while, the mordant bath becomes gross and murky, then I toss it down the drain.

I highly encourage you to start simple with your mordanting process and experiment from there. Though it may seem tedious, it’s necessary for those looking for a lasting, vibrant result. If you prefer to learn and experiment in a group setting, one of my dye workshops may be best for you! I announce upcoming events regularly on my email newsletter, click here to join!

As always, shoot me an email with any follow up questions. I’m happy to help!

Cheers,

Meg