Have you ever wondered why the pieces you pull from the dye vat are pale green and then magically turn blue? It’s due to the oxygenation of the dye. Wild Colours (the best resource ever) explains the process here, “When you expose the fibre to oxygen in the air you will see it gradually change colour from pale yellow to green and then finally to blue, as the indigo dye reverts to its insoluble blue form. Seeing the colour develop in the air must have looked like magic to many early cultures, and this change in colour can easily get you hooked on dyeing blues.”
This is one of the reasons I got hooked on Indigo, as it is truly magical to watch.