Lightfast Tests - testing natural dyes longevity
Note before reading: This blog was written in 2018, when I was studying for my MA (hence the Harvard referencing!). Where needed, I have edited these posts to correct any factual inaccuracies. This post was last edited Dec 2025.
This testing method is explained fully in my 2023 book Dyeing Yarn Naturally, available to buy in my shop or in all good booksellers.
Some natural dyes can fade over time. In order to create knitwear that has longevity, the colours need to last through many wears and washes!
In March I stuck 7 different swatches in between 2 squares of black card, the top one having a square cut out of it to let the light. This was following the suggested technique in Wild Colour (p64).
I left them on the windowsill in my studio for almost 2 months - slightly more than the couple of weeks recommended - because the weather was really bad in March and the beginning of April and so there wasn't much sunlight. The sun is strong in my studio in the afternoon and so the amount of light the swatches were exposed to was perhaps exaggerated, but this was a good 'stress test ' of some commonly used materials.
The dye materials tested were (L-R in left photo below): Onion skin, pomegranate skin, chlorophyllin, walnut, weld, avocado skins and weld. (Coreopsis was out of shot). These have all been alum mordanted apart from the walnut swatch.
As you can see on the right photo below, some materials fared better than others! Walnut and pomegranate look the same as before (perhaps due to high tannin content?) Weld and avocado (yellow and pink) have some slight discolouration. Coreopsis (orange has faded a fair amount), but chlorophyllin wins/loses the race with a very faded green! I will have to go back to the drawing board to dye a good green shade - perhaps the slightly longer process of overdyeing weld with indigo is the best option.
References:
Burns, R. 2018. Lightfast Tests 1-2. Photograph.
Dean, J. 1999. Wild Colour. London: Octopus.