Understanding Lightfastness in Naturally Dyed Cloth

Why Some Natural Colours Drift and Others Hold

Lightfastness is simply a measure of how well a colour resists change when exposed to light. It is not a single number but a spectrum, and natural dyes sit right across it. Indigo on wool may look much the same after a decade on a wall, while a turmeric-yellow cotton scarf can shift towards beige in a single bright summer. The difference lies in the dye molecule itself: how tightly it grips the fibre, how readily it oxidises, and how much energy is needed to break the bond holding the colour in place.

Fading is cumulative rather than sudden. A piece does not fade in one afternoon; it fades over thousands of afternoons. That is why a cushion left in a bright window for two years can look dramatically different from a sample of the same cloth kept in a drawer. Understanding this lets you make calm, practical choices instead of treating fading as a failure of your dyeing.

A Practical League Table of Natural Dyes

Most natural dyes fall into three loose groups. The following is a working guide drawn from experience rather than a laboratory, but it holds true across most fibres.

• Excellent lightfastness: indigo, madder root, weld, walnut hulls, cutch, pomegranate rind, and logwood on protein fibres when well mordanted.
• Good to moderate: cochineal, lac, fustic, onion skins, avocado stone and skin, rhubarb root and gallnut.
• Poor or fugitive: turmeric, safflower, brazilwood and sappanwood, most berry dyes, beetroot, and many flower-petal dyes such as hollyhock and dahlia.

Two cautions. First, indigo is unusual: it is lightfast but can crock, meaning it rubs off onto pale upholstery or clothing, and it often lightens at fold lines and edges rather than fading evenly. Second, "fugitive" does not mean useless. A fugitive colour can be beautiful in a wall hanging kept away from sun, or in a piece you fully expect to age.

Mordants, Fibre and the Chemistry Beneath

A dye only stays where it is chemically anchored. Mordants — alum, iron, copper, tannin — form the bridge between dye and fibre, and the choice of mordant changes both the shade and its staying power. Alum is the workhorse, giving clean and reliable results. Iron saddens colours towards greys and greens and can improve lightfastness in some dyes, but it also weakens cellulose fibres over time, so use it sparingly on cotton and linen.

Fibre type matters just as much. Protein fibres such as wool and silk generally hold dye more tenaciously than cellulose fibres like cotton and linen, which often need a tannin pre-treatment to reach comparable depth and durability. A well-mordanted wool will usually outlast an equivalent cotton by a comfortable margin. This is one reason traditional textile cultures put their most light-sensitive colours on wool and their indigo on everything.

The Light Itself: What Fades Cloth, and Where

Ultraviolet light does most of the damage, but visible light plays a part too, which is why even a north-facing room will slowly alter a delicate colour over years. Direct sun through a south-facing window in a British summer is the harshest environment most of us can offer a textile, and it is worth treating it that way.

A few practical points help. Ordinary window glass blocks some UV but not all, so a sunlit windowsill is still a fading machine. Older fluorescent tubes emit UV; modern LEDs emit very little, but brightness still matters, because fading is driven by total light exposure rather than heat. Distance matters enormously — light intensity falls away quickly with distance, so moving a piece just a metre further from a window can make a real difference over a decade. Rotating a piece every few months spreads the exposure and keeps the colour more even.

Display, Storage and a Few Habits That Help

You do not need a museum budget to protect naturally dyed cloth. You need a little forethought.

• Test before you commit. Keep a small swatch of every dye batch and pin it in a sunny window for a season. You will learn more from your own cloth than from any chart.
• Frame behind UV-filtering glass where possible, and keep a mount between cloth and glass so air can move.
• Rotate regularly. Swap a hanging every six months and store the resting piece flat, away from light.
• Store in the dark. Acid-free tissue in a closed box slows change dramatically; cotton bags are fine, plastic is not.
• Photograph when fresh. A dated photo is the only honest record of how far a colour has travelled.

For fugitive dyes, consider using them in pieces that live folded, boxed, or in a dim hallway rather than above a radiator or opposite a garden window.

Living With a Colour That Changes

Natural colour is not a fixed finish; it is a relationship with time. A madder red will deepen and settle, a cochineal pink will soften, an indigo will gently wear at the edges where it is handled. Slow stitching and natural dyeing both ask us to accept that the cloth we make will keep becoming something. Choose lightfast dyes where you need longevity — a quilt that will be washed and aired for decades, a garment worn daily, anything destined for a bright room. Choose the fugitives where you want their particular glow and can give them a gentler life.

Knowing which is which is the whole craft. The rest is simply paying attention, and enjoying what the light does to your work.