Sample of indigo dye, 1999.

A book of dye samples, c 1910.

A book of dye samples, c 1910.

'The Indigo Manufactory', 1777.

Beating indigo by hand, Allahabad, India, 1877.

Natural dyes shown with dyed fabrics and a model of a woad mill.

Indigo factory, Allahabad, India, 1877.

Indigo drying house, Allahabad, India, 1877.

Indigo beaters, Allahabad, India, 1877.

Sample of picric acid, (2,4,6-trinitrophenol), late 20th century.

A selection of early synthetic dyes and dyed material, mid 19th century.

Adolf von Baeyer, German organic chemist, late 19th century.