ESSTEBIO INDIGO BLUE
These are the blue dyes, especially indigo, derived primarily from the indigofera, isatis and polygonum species. Several species, especially Indigofera tinctoria and Indigofera suffruticosa, are used to produce the dye indigo.
Natural indigo is obtained by fermenting the leaves of various species of Indigofera, running off the and oxidizing it to precipitate the dye. The dye is precipitated by oxidation or by passing the air. The precipitated blue natural dye at bottom is dried in the air to make the cake. This is a vat dye and is used after converted into liquid form with sodium hydrosulphite and caustic soda in soft water. The dyeing is carried out in the reduced liquid form at about 25oC to 30oC. By oxidation, the dyed fabric slowly changes into blue colour form green.The process of dyeing of cotton, wool and silk is almost same. The appearance of dye is blue and main colouring compound is Indigotin.