This dye is manufactured from the dried roots of Rheum which is a traditional natural dye from China and Nepal. Rhubarb natural dye powder is easy to use and dyes excellent on protein and cellulose fibers alike. 
When dyeing with rhubarb natural dye powder, you should always do so in a well ventilated space and not inhale the fumes. Rhubarb (and the rhubarb family) roots contain a lot of oxalic acid which is not good to inhale.

Use at 5-10% WOF.
Active dye component; Emodin (anthraquinone), chrysophanol, oxalic acids, tannins.
Ph sensitive;
brick red (with an alkali modifier)
golden yellows (with an acidic modifier)
Green with ferrous sulfate post mordant.
Deep golden with copper mordant.
Bright yellow with alum mordant and a bit of vinegar in the dye bath.

100 grams of rhubarb will easily dye 1 kg of fiber.
Overdye rhubarb dyed fabrics with indigo for deep emerald greens.

Sustainably and renewable source, fair trade supply.