The Complete Guide to Buying Natural Fabric Dyes and Mordants

The vocabulary is what stalls most people getting into natural dyeing — alum acetate, tannins, exhaust baths, weight of fiber. Strip that away and the shopping list is short: natural fibers to dye, a color source, a mordant to fix the color, and a few dedicated tools. This guide covers what to buy, where to find it, and the order to do it in. Natural dyeing uses pigments from plants, insects, and minerals to color fabric — the same method used for thousands of years before synthetic dyes existed.

Start with the right fabric

Natural dyes bond to natural fibers and reject synthetics. Cotton, linen, hemp, wool, and silk all take color; polyester and acrylic will barely tint because their fibers are essentially plastic. Check the label before you buy or dye anything.

Do not start on expensive material. Dig through your own laundry pile or hit a thrift store first — plain white cotton t-shirts, old linen shirts, and cotton sheets run a dollar or two and are ideal for testing. Early results are often splotchy, and it is far less painful to learn on a $2 napkin than a new silk scarf. Fibers fall into two groups that behave differently: protein fibers (wool, silk) take color readily, while cellulose fibers (cotton, linen, hemp) need an extra tannin step, covered below.

Choosing your dye sources

Color sources range from free kitchen waste to purchased extracts. Beginners get the best results starting with scraps, which are forgiving and cost nothing.

Keep a bag in the freezer for onion skins and avocado pits; when it fills, you have a dye bath. For specialty colors, online suppliers such as Dharma Trading, Maiwa, and Botanical Colors sell extracts and dried plant material — buy small quantities to start, since a concentrated extract goes a long way. If you want to source your palette entirely from the kitchen, a dedicated guide to dyeing with kitchen scraps covers which foods yield which shades.

Why mordants matter

This is where beginners lose their color. You can dye cotton a brilliant yellow with turmeric, wash it once, and watch most of it rinse away, because the dye never bonded to the fiber. A mordant is a substance — usually a metal salt — that acts as a bridge between the dye molecule and the fabric, making the color washfast and more lightfast. You apply it to the fabric before the dye bath. The chemistry behind how a mordant fixes dye to fiber is worth reading once, but in practice it is just another soaking step.

Three mordants cover almost everything a beginner needs:

• Alum (aluminum potassium sulfate) — the safest, most common starting mordant. It brightens colors and improves lightfastness, and works on both protein and cellulose fibers (the latter with a tannin). Sold as "pickling alum" in the grocery spice aisle or by dye suppliers. Confirm it is aluminum potassium sulfate, not plain aluminum sulfate.
• Iron (ferrous sulfate) — a modifier that darkens and dulls, shifting yellows toward green and pinks toward purple. Use it sparingly; too much weakens fibers, especially silk. Bought from dye suppliers.
• Tannin — not a mordant on its own, but essential for mordanting cellulose fibers with alum. Tannins occur naturally in oak galls, sumac, and strong black tea. On cotton or linen you mordant with tannin first, then alum.

The tools you actually need

The rule that overrides everything else: once a pot, spoon, or bucket has touched mordants or dye, it never returns to food use. Label the whole kit clearly.

Build the set around a stainless steel pot in the 3-to-5-gallon range, reserved for dyeing only. A digital kitchen scale is genuinely necessary — natural dyeing runs on ratios calculated against the dry weight of fiber, so eyeballing produces inconsistent results. Add a heat source (a kitchen stove works, though an outdoor burner keeps dye smells out of the house), a wooden stirring stick, rubber gloves, a dust mask for handling powders, and a dedicated rinse bucket. Thrift stores are the cheapest source for the pot and utensils — a large stainless stockpot often turns up for around $15, and secondhand shops regularly carry them.

Handling mordants safely

Natural does not mean harmless. Metal-salt mordants are toxic if ingested and irritating with prolonged skin contact, and fine powders should not be inhaled. Work in a well-ventilated area — open windows, run a fan, or work outside. Wear gloves and a dust mask when measuring powdered mordants or extracts, and keep children and pets away from the supplies. Store mordants in clearly labeled, airtight containers away from food. Do not pour spent mordant baths down the drain; check local wastewater rules, or dilute heavily and disperse away from plants and waterways.

The workflow, in order

The sequence matters as much as the ingredients. Rushing any stage produces weak or patchy color.

1. Scour the fabric. Simmer it in water with a little soda ash or pH-neutral detergent for about an hour, then rinse thoroughly. This strips manufacturing oils and finishes that would otherwise block dye and cause uneven, patchy results. It is the most-skipped step and the most common cause of blotchy color.
2. Weigh the fiber. Record the dry weight of fiber (WOF). Mordant and dye quantities are calculated as a percentage of it — for example, roughly 10% WOF alum for mordanting, or about 50% WOF onion skins for the dye bath. Consistent ratios are what let you repeat a color.
3. Mordant. Simmer the scoured fabric in the mordant bath for about an hour, then let it cool in the bath, often overnight. For cotton and linen, do the tannin bath first, then alum.
4. Dye. Make the dye bath from your color source, add the mordanted fabric, and let it absorb — anywhere from an hour to a day or two depending on the depth of shade you want. Longer soaks give deeper color.

Temperature and water matter more than beginners expect. Most dye baths hold at a gentle simmer around 180°F rather than a rolling boil, since hard boiling can dull colors and, with protein fibers like wool, cause felting. Hard water high in minerals can also shift a shade, so if your results come out muddy, try distilled or rainwater for the next batch. Move fabric into and out of a hot bath gradually to avoid shocking wool fibers.

Keep a dye journal from the first batch: date, fiber type and weight, dye material and weight, mordant and weight, water volume, simmer and soak times, and a photo of the result. Without notes you will get a color you love and have no way to reproduce it.

Aftercare and realistic expectations

With proper mordanting, natural dyes are reasonably colorfast but rarely as bulletproof as synthetics. Wash finished pieces in cold water with a pH-neutral soap and keep them out of prolonged direct sun to preserve the color. Some dyes behave unusually well — indigo actually deepens and improves with age and wear. A single small item is a legitimate first project: a plain cotton bandana dyed with turmeric or a napkin dyed with onion skins takes two to three hours of hands-on time plus an overnight soak, and teaches the full scour-mordant-dye cycle on something you can afford to get wrong. Start on cheap thrifted cloth, keep the ratios written down, and treat the first few splotchy results as the cost of learning the process.