Fine bandhani silk comes from Western India, primarily Rajasthan and Gujurat, and is popular all over the subcontinent. These saris are traditionally worn to weddings and festive events, like garba.
'Bandhani' comes from the Sanskrit words 'bhandana' and 'bandha' which both mean 'to tie.' Bandhani refers to both the tie-dye method, known internationally by its Malay-Indonesian name plangi, and the finished fabric. The English word 'bandana' also comes from the same Sanskrit root words.
The special technique that creates the square patterns with yellow or white dots in the center that are characteristic of bandhani fabrics includes pinching up and resist tying areas of the fabric before dying. Dyers usually use a sheet of plastic pierced with pinholes to denote the spaces that need tying.
This sheet is held over the fabric and the dyer spreads geri, a water-based solution of red ochre, soot, or burnt sienna, over it with a sponge or rag. An imprint of the pinholes is left behind and workers, usually women and girls, will tie them using plain cotton yarn. They hold the tied fabric up by using the pointed nails of their pinkie fingers.
The parts of the fabric that are meant to appear as yellow or white dots are also similarly imprinted and tied. If there are other colors that are meant to appear in the fabric, the cloth will be retied after each subsequent dying.
In Gujurat the dying is done by submerging the cloth in a dye-bath, while in Rajasthan it's usually spot-dyed by hand.
Bandhani is also a fairly common technique that is applied to all sorts of fabric all over India. The rural women of Western India, for instance, typically wear cotton odhani shawls made with the bandhani method.
Traditionally, the bandhani squares are set against red and dark red and will form swirling or floral designs. Nowadays, though, you can find bandhani in every color of the rainbow and in a multitude of different patterns.
Bandhani fabrics tend to get more expensive the more knots there are tied into it, i.e. the more patterned it is and the more squares it has.
Fine Gujurati bandhani saris, known as garcholas, contains a patterned gridwork of tiny bandhani squares of yellow dots set against a bright red backdrop. Gharcholas can also be a large dupatta given to a Gujarati bride.
They contain lotus flowers, dancing women, and elephant motifs. These saris are highly detailed, and production centers in Kutch and Saurashtra.
Bandhani production is spread out over all of Western India and different regions are the best at different types of bandhani. Kutchi is a center for traditional bandhani work while Ahmedabad is where most of the cheap and affordable bandhani is produced.
In Rajasthan, the finest bandhani is made in Bikaner. There needs to be a river by the towns were bandhani is produced in order to rinse out the dye.
Generally, more colors are used in Rajasthani bandhani than in Gujurati.
To tell if a bandhani sari is genuine bandhani and not a printed imitation, it should be sold with its ties still intact. Then you have the excitement of pulling the thread out to see the full design.
Sources: Indian Textiles by John Gillow & Nicholas Barnard