Weld Yellow

Weld plant in a garden with a trug of leaves in front.
Weld in our garden

Weld is a tall plant with tiny yellow flowers that was the preferred source of yellow dye in the western European middle ages. It’s an annual and very easy to grow (in mid-Canterbury, NZ) from the tiny black seeds that it produces and I have found that it’s well established by self seeding in my garden, having planted perhaps half a dozen plants several years ago.

I have found that the best time to pick them for dyeing is in December, before the leaves start to brown off. They have started flowering but are not all going to seed quite yet. Obviously if you want to leave a couple you can then gather seed from them.

I pull them fully out of the ground, they have a tap root so generally come quite easily, and then I strip the leaves off them and throw the stalk and flower heads into the compost.

I fill a large (old 10L aluminium preserving pot) pot with leaves, half fill it with water, and cook for an hour or until the leaves are thoroughly wilted. I’m a fan of leaving them to cool overnight but this isn’t necessary. Remove the leaves, squeezing them out over the pot to capture as much of the dye liquor as possible. Then strain the rest – you want to remove as much of the plant material as you can. I use either a muslin cloth in a colander and/or a sieve, depending on quantity. Throw the mushy leaves in the compost.

Fibre preparation

I always mordant my fibre as it helps the dye stick and last longer. My go to mordant is Alum (cheap from a garden shop) with Tartaric acid (which you can get at the supermarket):

  1. weigh the fibre, yarn, cloth you are going to dye.
  2. calculate 10% of this weight for your Alum.
  3. calculate 5% of the fibre weight for the tartaric acid.

Put the alum and acid into your mordanting pot with sufficient water to keep your fibre mobile, bring to a good simmer while you soak the fibre in warm-hot water and ensure its thoroughly wet. (This ensures no air bubbles form around the fibre preventing the mordant from getting in and stops you from ‘shocking’ it when you add it to the simmering mordant.) Add the fibre to the mordant and simmer, stirring occasionally to ensure it all gets evenly treated, for one hour. Again I often then allow it to cool a little in the pot, possibly overnight, but you don’t have to.

Dyeing

Once your fibre is mordanted bring your dye liquor up to heat and add an alkali moderator. I used 10 gram of washing soda (Sodium Carbonate Decahydrate) dissolved in a little water and the colour shift to a brassy gold was instantaneous. Without this I have only ever gotten pale lemony yellows that weren’t very attractive (see image below).

I have found that weld likes it hot so bring it to a good bubble before adding the mordanted fibre and keep it at around 95 C. Keep it at this temperature for at least an hour, then as before you can simply turn it off and allow to cool in the pot, or remove it from the dye hot.

Give it a couple of rinses in warm-hot water (it can be a bit cooler than the dyebath but don’t shock it) and then a quick wash before drying in the shade. Strong sun may change the shade a little.