$7.00 per 50gms
The chemical formula for natural and synthetic indigo is the same but synthetic indigo is almost pure indigotin. Natural indigo has a high proportion of impurities and gives variations in colour whereas synthetic indigo gives an even blue that never varies.
For experienced dyers. A vat needs to be made.
For a great recipe book, we recommend two books, either The Ashford Book of Dyeing