I found these beautiful grapes at a local market. The taste amazing and the skin shines a lovely deep red black in the sun. They are called Midnight Beauty. Sadly they are seedless, so no growing my own.
I'm saving the skins in the hope of making a fermented dye, the flesh is too nice to waste.
Fermented dyes are a new thing for me. The idea is to extract the anthocyanins (water soluble pigments) which often dissipate with heat. Fermentation processes extract the dyestuff without degradation.
Dying on silk and wool should work best, however cellulose fibres can be used to with a soy milk protein bath.
Some dyers also ferment their wool, with the dual hope of softening it to the touch as well as creating a rich deep colour.
My method is to fill a shallow wide jar with the skins and a handful of past their prime blueberries, cover with water an allow the sugars and yeasts already on the fruit to do their work. Importantly I'm not going to seal the jar, just cover with a bit of plastic wrap pricked by a pin to release the gasses.
Grapes and berries aren't the only thing that you can use as a dyestuff with this method. Some research has gone into purple potatoes, flowers, cabbage, wood chips, coconuts/candle nuts, lichens and sap.