The crottle is put into the bath with a sufficient quantity of water, boiled up, allowed to cool, then boiled up with the wool until the shade required is got.    From Wordnik.com.  [Vegetable Dyes Being a Book of Recipes and Other Information Useful to the Dyer] Reference

Other dyers use it in the following way: A layer of crottle, a layer of wool, and so on until the bath is full; fill with cold water and bring to the boil, and boil till the colour is deep enough.    From Wordnik.com.  [Vegetable Dyes Being a Book of Recipes and Other Information Useful to the Dyer] Reference

Oak-rag, Hazel crottle, Rags.    From Wordnik.com.  [Vegetable Dyes Being a Book of Recipes and Other Information Useful to the Dyer] Reference