Making Weld Dye from the Plant to the Wool

Weld appears in all the dye books, usually commended as giving a good clear yellow and being one of the most light fast plant dyes.  Though it is described as a wild plant, I've not seen any round here, despite keeping pictures in my bag for reference when walking the dog. She's pretty slow these days and glad of a little sit down, so I have plenty of time to check the hedgerows.  No luck last summer, so I sowed my own.  In this picture, the weld plants are the tall spikes in front of the purple chive flowers.  If you see any locally, grab them.  Books list dozens of sources of yellow. This dye plant is not just one among the many, it is a total power house, Olympic champion, packs a punch like Katie Taylor.

The Latin name is Ruseda luteola, after the luteolin pigment it contains.  Weld grows from seed as a biennial.  Past gardening experience has showed me that if you can get biennial seeds to germinate in trays in the late summer, then plant them in the garden in early autumn, the following spring they often behave as if they were in their second year and flower for you very nicely.  Strictly speaking, you are supposed to sow these seeds in spring and not transplant them, because they have a tap root.  Still, here's one of mine in March, looking small and battered after the winter. 
As you can see from the top photo, my patch of autumn sown weld plants has now shot up flowering spikes.  Harvesting instructions conflict.  One book suggests picking leaves off the first year rosettes, Jenny Dean advises taking the flowering spikes, some blogs show enormous plants with multiple side shoots.  This paper studies dye yield from weld grown in Italy. The conclusion I drew from it was that if I left the plants to grow longer, although I would have a bigger weight of plant material, the concentration of dye in it would be lower. So, last week, I chopped off the leading spikes with the tiny flowers just coming, leaving the lower part of the plant to carry on putting up side shoots, just as Jenny Dean advises.

There are a multitude of methods described for extracting dye, ranging from just scalding fresh chopped leaves with boiling water and leaving them to soak, to fermenting them for a week, then boiling for an hour.  People don't always specify if they are using fresh or dried material.  I split the difference, giving 40g of my fresh leaves two days in cold water, then half an hour simmer.  A piffly little quantity in the colander for an equal weight of wool, mordanted with Alum and Cream of Tartar.  The consensus seemed to be that a one to one ratio is enough. The rest of my spikes were hung up to dry.  One major objective of this summer's season is to preserve material for winter projects.  The second objective is to have a fair idea of what colours to expect. The third is to know how quickly they will fade.

The soaked leaves did not flood the water with colour and even the simmer did not produce much apparent dye.  I ummed and aahed about putting in a whole 40g of wool, then went for it, leaving the bag of leaves in the bath.  


After 24 hours cold soak, the first skein was an astonishingly bright yellow - far left.  I put in another 40g skein, this time I brought the bath up to a simmer, left it overnight and next day, skein two was strongly yellow.  Same again with skein three - far right - and that little handful of 40g chopped fresh leaves and stalk still gave significant colour.  Given this power, the 350g bunch I have drying should give a strong yellow to 1kg of wool.  I have never seen anything so strong as this before.

No real need to bring up the yellow with an alkali afterbath, but just to see what would happen, I put a bit of each skein in water with half a teaspoon of soda ash for half an hour.  Dizzyingly vivid!

Weld may even predate woad as a dye plant.  It is certainly easier to get the colour out of it.  These results guarantee it several square feet of earth in my garden.  Nine days after cutting the main spikes, the side shoots are almost in flower and ready to be cut again.  There could even be a third lot to come.  So long as the dried leaves work half as well, I shall have sunshine in the depths of winter.

Afterword mid July

                                                                                                                                                                                                                       I found wild weld! 

Not locally, but on an industrial estate I happened to be walking through.  It certainly does cope with poor soil, though these plants are shorter and smaller than mine on the veg patch.  I had read weld likes freshly turned earth, and saw it had grown on the bald patches by a new building, but was not among the established verges of wild plants nearby.  In future, I shall try looking around building sites and road works.