A dye journal is the least glamorous piece of kit in a natural dyer's cupboard, and the one that saves the most money. Every season we simmer weld, madder and nettle, pull out a beautiful colour, and then by the following spring have entirely forgotten the mordant percentage, the plant weight and whether that particular gold survived a summer on the windowsill. A few minutes of note-taking after each bath turns a pleasant afternoon into useful knowledge.

Start with a Page per Dye Bath

An A5 hardback notebook is ideal, or a ring binder with one page per dye lot. Keep the format identical every time so you can compare entries at a glance. You want, at minimum:

• Date and the weather that week — drought and late frost both change dye content in plants.
• Plant name, Latin and common, plus which part you used (leaf, flower, root, bark, berry).
• Fresh or dried weight, in grams, and how much fibre went in with it.
• Fibre type — wool, alpaca, silk, cotton, linen — and the weight in grams.
• Mordant, percentage (percentage weight of fibre, usually written as WOF) and any adjunct such as cream of tartar.
• Water: rainwater, tap, hard or soft, and the pH if you checked it.
• Method and timings: cold soak, simmer, temperature, how long, whether the bath was strained.
• Result: a colour description in plain words, plus a swatch.

The habit that matters is writing it down while the pot is still on the stove. Memory is astonishingly unreliable about whether you used 10% or 15% alum.

Record the Whole Recipe, Not Just the Colour

"Yellow" tells you nothing. "Weld, 200g fresh flowering tops to 100g alum-mordanted wool, simmered 45 minutes, gave a clear lemon yellow; second exhaust bath gave a softer primrose" tells you everything you need to repeat it or adjust it.

Note the small variables too. Iron at 2% will sadden weld to a khaki-green; the same bath with a splash of washing soda after dyeing can shift a madder red towards coral. Hard water in chalk and limestone areas dulls some colours and brightens others, so write down whether you used rainwater. If you keep your mordant baths and reuse them, note how many times — the third alum bath behaves differently from the first.

When a colour disappoints, record that as carefully as a success. A feeble result from dried yarrow in November is worth remembering, because it stops you harvesting the same disappointing bundle next year.

Testing Lightfastness Without a Laboratory

Most natural colours fade; the useful question is how fast, and in what direction. You do not need a blue wool scale card to get a workable answer. Cut two small swatches from every dye lot. Keep one in a drawer as your reference. Pin or tape the other to a south-facing windowsill, uncovered, and leave it for six weeks through summer.

Then compare the two and write a simple note: "no visible change", "slight shift towards grey", "faded to half strength", "madder barely moved". Give the test a start and end date, because a July windowsill in Devon is not the same as a February one in Aberdeen. Over a couple of years you will build a personal ranking — typically weld and madder hold well, while some flower-petal dyes from mallow or elderberry fade quickly to buff. That ranking should decide which colours you put into a jumper and which go into cushion covers kept out of direct sun.

Plant Yields: The Numbers That Shape Next Year's Beds

This is where wildflower gardeners have a real advantage, because you know exactly what you grew. For every harvest, jot down how many plants you cut, the area they occupied in metres, and the fresh weight you carried to the pot. Then note the dried weight after a week in the airing cupboard or shed — the ratio is often three or four to one, and it is the single most useful figure for planning.

Some worked examples worth recording for your own conditions: a well-grown two-metre row of weld might give you a kilogram of fresh flowering tops, enough dye for several hundred grams of wool. Lady's bedstraw roots need three years before they are worth lifting, and a square metre yields far less than you would hope. Woad leaves from a first-year rosette, cut in August, give a small but genuine blue. Write down what your soil actually produced, not what a book promised.

Swatches, Photographs and the Weather

A written description is good; a physical swatch is better. Wind a metre of the dyed yarn onto a small card, punch a hole, and tie it into the notebook with the entry date. For fabric, cut a 5cm square and stitch it to the page. Keep the same fibre type across entries where you can, so comparisons are fair.

Photographs are a useful supplement if you take them in daylight, out of direct sun, with something neutral in the frame for reference. Never rely on a photo alone — cameras flatter some yellows and deaden some greens.

Turning Notes into a Seed Order

In January, read the journal from cover to cover with a cup of tea and a seed catalogue. Score each plant on three things: the colour you actually got, how well it held up to light, and how much ground it needed for that result. Anything scoring well on all three earns more space. Anything that needed a square metre of bed for a pale, fleeting tint gets a polite reduction.

Then look for gaps. If your greens are all iron-saddened and slightly muddy, plan to grow more weld for overdyeing. If your blues came out thin, consider a second woad bed or sowing more Japanese indigo. Add a note to each entry about what you would change: "try 15% alum next time", "harvest before flowering", "use rainwater only". Next autumn you will thank this year's self for the detail.