- Purple: From the woad plant (Isatis tinctoria)
- Blue: From the indigo plant (Indigofera tinctoria)
- Green: From the yellow of the weld plant (Reseda luteola) mixed with the blue of the woad plant
- Yellow: From the weld plant (Reseda luteola)
- Red: From the madder plant (Rubia tinctorum)
- Brown: From walnut husks
- Black: From oak bark or iron sulfate
- Orange: From the lichen Parmelia saxatilis
The Celts would gather these plants and prepare them by boiling or fermenting them. They often added various mordants, such as alum or vinegar, to the dye mixture to help the dye adhere to the wool. The wool was then steeped in the dye mixture for several days or weeks. The longer the wool was left in the dye, the deeper and more vibrant the color would be.
Once the wool had been dyed, it was rinsed thoroughly and hung out to dry. The dyed wool was then ready to be spun into yarn and woven into fabric.