For my work for The Power of Stitch I am trying to depict the power of nature through volcanic activity, so I wanted a bright red. A bright red is not easy to get with natural dyeing, but fermentation dyeing works well with madder.
I put 100 grams of ground madder in a 4 pint plastic bottle and filled nearly to the top with water.
Every day I removed the lid to let any gases out and gave it a good shake. Madder works better in a high PH and fermentation tends to make the dye acidic so after a week I added a teaspoon of slaked lime.