SCOURING AND MORDANTING
Scouring and mordanting are two essential steps to prepare a textile for natural dyeing. These process are the foundation for even, permanent color, and are necessary for a dye result which will withstand washing, wear, and light exposure.
The following instructions apply to plant fibers (cotton, hemp, bamboo, linen) only. The scouring process for animal fibers (silk, wool) is different. Plant fibers are my area of expertise, so I innvite you to do your own research on these processes if you’re working with animal fibers.
Scouring
Scouring is the process of processing a textile to remove sizing, wax, dirt, or other contaminants present from the manufacturing process, gently stripping and readying the fibers to absorb mordant and dye.
This process is specifically done with soda ash (a.k.a. sodium carbonate), not regular detergent. Soda ash is a naturally occurring compound with gentle alkalinity, historically sourced from the ashes of plants growing in sodium-rich soils, which is where the common name comes from.
Materials:
Non-reactive* dye pot or food-grade bucket **
Measuring spoons **
Stirring spoon **
Kitchen scale (measures in tenths of a gram, e.g. 10.5g)
Cooking thermometer
Instructions:
Measure out soda ash at 1-2% the dry weight of fiber (WOF). (If fiber weight is 100g, measure out 1-2g of soda ash.)
Fill a dye pot or bucket with the hottest possible tap water, allowing enough room for the textile to move freely.
Add soda ash and stir until completely dissolved.
Add textile to the bath and immerse completely, rotating it gently and consistently, ensuring the textile remains completely immersed in the bath.
Leave the textile in the bath until it’s cool enough to handle.
Once at room temperature, remove the textile and rinse thoroughly with same temperature tap water.
Gently wring out excess water from the textile and proceed to mordanting.
NOTE: If scour bath is very cloudy or dirty when finished, repeat the scouring process.
Mordanting
A mordant (French for “to bite”) is a substance applied to a textile that acts as a link between fiber and dye, allowing the two to form a permanent chemical bond. Without a mordant, natural dyes typically form only loose chemical bonds with a textile, and are likely to result in little to no color, or in color that fades or washes out quickly.
The most common and effective mordant for use on plant fibers is alum, a naturally occurring mineral used as far back as Ancient Egypt. Today, “alum” refers to a number of preparations of mineral aluminum; I use aluminum potassium sulfate. In its various forms, alum is used for dyeing, paper making, leather tanning, water purification, and even pickling foods. Combined with a source of tannin—I typically use oak galls, either prepared extract or foraged from the wild—this historic mordant process yields permanent, saturated colors on cellulose (cotton) fibers.
Materials:
Kitchen scale (measures in tenths of a gram, e.g. 10.5g)
Non-reactive* dye pot or food-grade bucket **
Stirring spoon **
Cheesecloth or mesh drawstring bag
Hot water
Cooking thermometer
NOTE: Alum is a fine powder that can be corrosive to skin and is harmful if inhaled. Please wear gloves and a mask when handling alum, and work in a well-ventilated space.
Instructions:
Weigh the piece(s) you’ll be dyeing and measure out 10% of the WOF in oak gall extract. (For 100g of fiber, use 10g oak gall extract.)
Dissolve the oak gall extract in a bucket or dye pot of room temperature water, stirring well to break up any clumps.
Immerse your damp, pre-scoured textile(s) in the oak gall solution, stirring regularly and ensuring they remain fully submerged, for one hour.
(Leave your piece(s) in until you’ve prepared the next mordant step (alum). Removing from the bath and exposing the tannin to air will cause oxidization, which may result in discoloration.)Measure 15% of the WOF in alum. (For 100g of fiber, use 15g alum.)
Dissolve alum in a bucket or dye pot full of the hottest possible tap water.
Submerge your textile(s) in the alum solution, working quickly from tannin to alum (do not rinse in between). Stir regularly and ensure they remain submerged, 1-2 hours.
Proceed directly to dyeing, or let your mordanted goods dry completely before storing and use within 3 months.
Local Tannins (Mordants)
Tannins are substances found in many plants which can act as natural mordants, binding dyes to fabric more permanently. In my dye work, I prefer to layer on as many tannins as possible, a technique which enhances color permanence. I use alum and other purchased mordants, as in the tutorial above, but I find it extra fulfilling when I can complete a project using just what’s around me.
Some plants contain tannins and other colorful compounds. For example, pomegranate skins are tannin-rich, but also have generous flavonoids, and they produce a strong yellow dye. Alone, certain kinds of tannins are nearly colorless, and these are what I seek out for mordanting.
My favored local tannins are oak galls and laurel sumac. Species of oak (Quercus) and sumac (Rhus) grow around the world, so it’s highly likely you’ll find relatives of these plants near you. If not, ethnobotany texts can once again be helpful. Seek out any local plants that may have once been used for tanning leather—they contain strong tannins (see the etymology there?) which will likely function well as mordants.
Materials:
Collected tannin-rich plant material
Kitchen scale (measures in tenths of a gram, e.g. 10.5g)
Non-reactive* dye pot or food-grade bucket **
Stirring spoon **
Cheesecloth or mesh drawstring bag
Heat source (stove)
Wild Tannin Mordant Recipe
Gather tannin-rich material like oak galls, acorns, sumac leaves, acacia pods, eucalyptus bark, chestnuts, etc.
Weigh your wild tannin material, and measure out 25-30% of the WOF that you’d like to mordant. (e.g. to mordant 100g of fabric, measure 25-30g of plant material.)
Crush, chop, grind, or otherwise process your tannins into small pieces. Tie everything up in a cheesecloth bundle or contain in a fine mesh drawstring bag.
Fill a stainless steel or enamel dye pot with water, heat, and simmer your tannins for 30 minutes to an hour, depending on the hardiness of the plant material. The water should take on a slight (tan-to-yellow) color.
Introduce pre-scoured, damp fabric into the tannin mordant and submerge completely.
Keep the mordant bath at a low simmer. Leave your fabric immersed and stir regularly for even mordant uptake, about an hour.
Remove fabric from the bath and let it briefly cool to air temperature, then rinse immediately in fresh water. (Leaving unrinsed tannin can sometimes result in oxidization and discoloration on the fabric.)
Tip: Test the strength of your tannin mordant by soaking an unmordanted piece of fabric in the tannin liquid, then introducing it to an iron modifier; either using powdered iron or my Wild-Harvested Iron recipe (below). The darker the resulting color (probably a purple-gray tone, maybe a brown or green tone), the stronger the tannin.
Wild-Harvested Iron (Modifier)
“Foraging” usually refers to gathering plants or other natural materials from the earth. But in this case, foraging acts as a kind of trash removal, since we’re actually looking for manmade stuff—rusty objects, which contain iron oxide.
Note: Forage for rusted objects safely, wearing heavy duty gloves. Even small injuries from rusted objects can be dangerous.
Rust—iron oxide—occurs when iron reacts with oxygen and water. Prepared the right way, we can utilize this form of iron as a powerful natural modifier, which reacts with tannins present to sadden dye colors (e.g. sunny yellow turns olive green; petal pink turns dusty purple).
Materials:
Collected rusted objects
Mason jar **
White vinegar
Cheesecloth
Sieve
Foraged Iron Modifier Recipe
Wearing heavy-duty work gloves, collect enough small rusted objects to fill a lidded jar.
With the rusty goods inside, fill up your jar most of the way with water. Top off with a splash of white vinegar. (The vinegar is what chelates the iron, making it water soluble, and available to us as a modifier.) The liquid in your jar should cover all the rusty pieces with little room at the top.
Seal the jar with a lid and label it with contents and date.
Once a day, give the jar a good shake. The iron solution is ready when the liquid inside is approximately the color of rust (after about a week).
When ready to use, strain the liquid through a fine sieve lined with cheesecloth to eliminate any big particles. Dilute with water to use as a modifier bath, or use the concentrated liquid for “painting” on fabric. (Undiluted this liquid is very potent, so you’re likely to get gray colors or even blue-blacks.)
* Stainless steel or enamel are considered non-reactive cookware. “Reactive” metals like aluminum, iron, tin, or copper (and more) will alter dye results.
** All kitchenware and utensils used for dye projects should be reserved for dyeing only. It’s dangerous to prepare or consume food made with pots or utensils that have come in contact with substances used for dyeing.