The manufacturing process for blue indigo dye is a true art form and a real labour of love. Indigo is derived from the botanical Indigofera tinctoria which is a sub-tropical shrub that grows to a height of around 1-2 metres. The leaves from matured plants are harvested and left to soak in a traditional tank with a depth of about 2.5 feet (0.3m). The soaking process leads to a natural fermentation, and after approximately 15 hours, the green pigment from the leaves diffuses out to form an extract in the water. Sometimes this green extract is dried and used as a pure form of dried indigo leaf powder. However, to form the distinctive blue indigo concentrated dye, the leaf extract is taken to another “stomping tank” where it is agitated and oxidised by the manual movement and kicking by the workers legs. This manual kicking is hard work, and continues in the tank for 2-3 hours eventually forming a bright blue indigo precipitate which has a thick consistency. The colour comes from the natural colouring in the plant called Indigotin. This thick colloidal indigo is then boiled in a copper vessel to evaporate off the water, filtered and then pressed into a large flat cake (rather like a slab cake). This cake is cut into squares and then each square is naturally dried in the sunshine. Here we have the finished indigo dye cake. To make the powder the dye cake is crushed in powder rollers to form the finished indigo blue dye powder. The cakes are excellent as they make for a beautiful novelty gift, can be crushed into powder, or used as they are for art work (similar to the use of charcoal). Even though the blue dye is harmless, gloves are advised when handling the indigo dye cake.
These dye cakes are concentrated with an Indigotin strength of between 40-45%. When used as a dye for cotton, wool and silk, the process is very much the same with vat dyes where the dye has to be dissolved in an oxygen reduced state by using an oxygen reducer, and then re-oxidised in air to get the desired shade of blue.
Please note these are a natural, handmade product so not all cakes are uniform is size and shape. Some also may be in several chunks. In any case, a total weight of 100g will always be supplied in a cardboard presentation box.