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Ground, dried leaves of a small tree native to the Mediterranean, Rhus coriaria. This has been used for tanning leather for centuries, producing a yellowish-green colour. It was once widely used in the woolen trade to produce shades of brown through tan to yellow-brown and olive and is sometimes called Tanner's Sumac. Used mainly on protein fibres but worth experimenting with on cotton and other plant fibres. We can't find much information, but suggesting trying this at 20-30% WOF for medium shades, as a starting point.. TO USE: soak in warm water overnight. Simmer in liquid 30-60 minutes at 170-190°F. Cool, strain, add more water if necessary then simmer premordanted fibre for 30-60 minutes at 170-190°F. Lower temperatures (below 160°F) may help the yellow pigments to shine through, and keep down the brown tones. Light and washfastness: probably good to excellent with a mordant.