Natural Dyes
Having colourful clothing on your character is a good way to indicate who they are, where they come from, and how wealthy they are. Are they wearing undyed cloth? Cotton? Linen? Wool? What kind of climate are they in? What kind of dyes are available to them? Are they going to go to a market and buy cloth pre-dyed? Are they going to buy clothes pre-made?
For one of my characters, she’s forced to rely only on herself to colour the plain white linen and cotton and wool clothes that she has. I had her use berries to dye her shirts blue, and then had to find out what people used back in the day to dye things. I also had her come from a background where she hadn’t ever dyed anything herself, and so she had to rely on her memory and experimentation to see what she could use.
Fixing your Cloth
One thing I learned was that dying was a bit of a hit and miss process. Professional dyers used substances called Mordants to fix the dye to the cloth, and often pre-mordanted their material before dying it. Common mordants were metallic salts such as copper, iron and alum – the latter being the best as it has no effect on the final colour of the dye.
A good resource is this one: Medieval Mordants
A key ingredient was also ammonia, which was available in the form of stale urine. There are accounts of dyers in towns being forced to live on the edges of the town and downwind of everyone (just like tanners) because of the urine being used – and people used to donate their chamberpots to the tanners and dyers in the morning!
My character used a combination of rock salt and urine. Of course this may not have been what dyers actually used, but it would produce a kind of mordant that may not be 100% fixed, but would at least last a few washes!
Colours
My character used berries, boiled for an hour with the cloth, to dye her clothes blue. Due to the fact she’s in a fantasy world that’s loosely based on Europe, I didn’t have her collect Woad leaves… I just made up a berry that would suit. Yay for fantasy!
I also had her talk with another girl about what she used, and learned about blue from Woad, and red from Madder root, and yellow from onion skins or the inside of Madder.
A good basic idea of colours was as follows:
red – madder root rubia tinetorum, kermes or grana from insects
blue – woad leaves isatia tinctoria
violet – orchil from lichen
crimson – brasilwood from the East India tree
purple – brasilwood from the East India tree
yellow – weld dyers’ rocket, turmeric, saffron, onion skin, marigold, chamomile
green – indigo, weld, turmeric (often yellow that was overdyed with blue)
brown – walnut shells, bark
You can read more here: https://rosaliegilbert.com/dyesandcolours.html
The substrate (base material) was also a factor in colour. Cotton and linen take up colour differently to wool and silk (the latter being animal based rather than plant based) and of course leather was also dyed differently. For a dark black wool, a brown wool from a naturally brown sheep was dyed with woad blue. My character was dying some cotton and linen shirts, which were a base of white, and so ended up with lighter blue and darker blue, depending on how deep they were in the dye, how long they were in there for, and in some cases, they were patterned based on how twisted the cloth ended up!
For a good plain dye, remember that most dyers dyed the actual fibres before the cloth was even woven, just like in the picture above.
Resources
If you’re looking for a deeper read, try these places:
How to grow your plants:
https://www.gardeningknowhow.com/ornamental/foliage/madder/growing-madder-for-dyes.htm
https://www.gardeningknowhow.com/ornamental/flowers/woad-plant/picking-woad-leaves-for-dyeing.htm
http://www.allnaturaldyeing.com/madder/
Medieval Dying:
https://thehistoryvault.co.uk/medieval-textiles/
And Wikipedia… kindof goes without saying.