First of all we all stood around the cauldron like witches.
In the dye bath the indigo is yellow, or it should be so long as you keep the oxygen out. As you can see it was beginning to oxidise.
Then after casting our spell we retrieved the wonderful piles of mystical fabric, which come out of the cauldron yellow, not blue. Exposure to the oxygen makes them turn blue.
It's pure alchemy!
And, in preparation for my next trick, a bit of paper cutting to make repeat patterns.