Sydney’s has always been fascinated by indigo blue. Indigo, largely associated with the colour of denim, is amongst the oldest dyes to be used for textile dyeing and printing. Historically, indigo was a natural dye extracted from plants. This process was once very important economically because blue dyes were quite rare. It is believed that indigo dyeing started in India, the earliest major center for its production and processing. Today, several thousand tons of indigo is produced each year, though it is done so synthetically. It is the blue of blue jeans.
Chunked natural indigo. Source: Natashalh
Indigo dye is a quite tricky to work with as it isn’t water soluble and doesn’t bind to fabric unless the dye vat is deprived of oxygen.
Interesting fact: Urine is sometimes used in the indigo dyeing process as it provides the alkalinity that the indigo needs, and it ferments and therefore depletes oxygen in the solution.