Known in natural medicine, but also a great dyer. Rich in tannins, about 30-40%.
Use 50-100% wof, always soak barks before heating to fully release the tannins. Heating is needed. Boiling will dull the hues.
No mordant is needed, but alum will give more yellow, copper will yield soft orange hues.
This is a sustainable and renewable source of dye from Europe. Organic.