Wash and Rub Fastness: Testing the Colour Before You Trust It

Cut two small pieces of the dyed fibre. Keep one as the control, somewhere dark. Take the other and pin a piece of undyed white cotton or wool against it. Wash both together in water at 40 C with a little neutral detergent, worked gently for half an hour, then rinse and dry them flat. Then read two things: **The sample against the control.** How much paler has it gone? A little is normal; a lot means dye that was never bonded. **The white witness.** How much colour has moved onto it? This is the number that matters for a garment, because it is what will happen to everything else in the wash. The witness is the part beginners leave out, and it is the half that predicts the disaster. A skein can hold its own depth perfectly and still ruin a load of washing.

Rub a piece of dry white cotton firmly against the dyed fibre, ten strokes, always in the same direction. Then wet a second piece and do the same again. Look at both white pieces. Any colour on them is colour that will come off on skin, on a shirt collar, on a chair. The wet test is nearly always worse than the dry one, which is why it is worth doing both. **Indigo is the famous case.** Indigo is held mechanically in the fibre rather than bonded to it, so even a well-made indigo crocks — and that is exactly what produces the worn highlights on old denim. It is a property of the dye, not a fault in the work, and it can be reduced but not removed by thorough rinsing and by not building the depth too fast. **Heavy shades crock more than pale ones**, in every dye, because there is more surface dye sitting on top of what actually bonded.

A note saying "faded a bit" is worth nothing six months later. Use a scale and keep the samples. The textile industry uses a five-point grey scale where 5 is no change and 1 is severe change. A home dyer can use the same five points honestly by keeping the control alongside: **5** — no difference visible against the control. **4** — a difference only visible when they are held touching. **3** — clearly different, still obviously the same colour. **2** — strongly changed. **1** — a different colour. Score the sample and the white witness separately; they are different numbers. Staple both pieces and the control to the record card. The stapled scrap is the measurement — anything written down is a description of it.

Poor fastness has a small number of causes and most of them are fixable next time. **Overloaded bath.** More dye was used than the fibre could bond, so the excess sits on the surface. Symptom: rinse water that never runs clear, heavy crocking, big loss in the first wash. Use less dye, or ladder a second skein through it. **Under-mordanted.** Especially cellulose without a tannin step. Symptom: pale result and most of it washes out. **Struck too fast.** Hot entry, so the dye grabbed the surface instead of penetrating. Symptom: uneven as well as unfast. **Not rinsed properly.** Symptom: colour in the first wash and then nothing much afterwards. This is the cheapest one to fix, and a proper rinse — until the water runs clear, at bath temperature — is part of the dyeing, not the tidying up. For an existing skein that crocks, more rinsing genuinely helps. A wash in warm water with a little detergent removes surface dye and the skein ends slightly paler and much better behaved. Do that before it is knitted, not after.