Reseda luteola (weld or dyer's weed) is a traditional dyeing plant that gives splendid yellow colours. The substance that gives the yellow colour is luteolin, a so called flavonoid, and is present in the whole plant. Reseda is known for its good washing fastness and light fastness, meaning that the colours won't fade easily under the influence of water (washing) or sunlight. However, the fabrics that are to be dyed have to be pre-treated with a mordant.
