The dyes made with the roots of different barberry species (there are quite a few) are considered alkaloid dyes. While the European species never gained much fame for their dyeing properties, the fruit is still much loved in jellies and jams. In Asia and America the use for fibre dyeing has been common and wider spread for centuries.
 
In Asia the dye is often used together with Turmeric to improve light fastness of the fugitive but oh so vibrant Turmeric.
In the Americas the use of Barberry roots and twigs is known by the Navajo, Mapuche, Apacje and Mescalero peoples.
 
The active dye component berberine is found in the plant in the form of a salt, which does not need a mordant to attach itself permanently to fibers. We are using the stripped bark of the roots for dyeing.
 
Active dye components; 
Berberine
Palmatine
Berbamine
Colourfastness; good
Use at 10-20% WOF for a medium shade. Barberry is a very economic dye stuff.
Soaking the bark overnight will maximize the results. Slowly heat the bark in the dye pot with the fibers, keep the dye bath below boiling. Dye for around 1.5 hours and let the fabric cool down in the dye pot.
Mordanting is not nescesary but using different mordants before or after the dye process will give different shades.
Samples dyes at 12.5% WOF.
 
Barberry is a sustainable and renewable dye source.