- Birch leaves are collected in spring and dried in the dark.
- They come from the two birch species Betula alba and Betula pendula from the family Betulaceae.
- These birch species are native to northern Europe and the temperate latitudes of Asia and grow mostly in deciduous forests, meadows and bogs.
- Birch leaves contain the flavonoids hyperoside and a myricetin galactoside as coloring ingredients. It also contains about 3 to 5% tannins.
- The colors that can be obtained range from golden yellow to olive green.
- Wool pre-stained with alum becomes a beautiful bright yellow, if the material is treated with iron or copper sulfate, the tone changes to olive when exposed to air.