Indigo was the most important of the natural dyes. As it was light-fast and eminently suitable for cot
Adolf von Baeyer (1835-1917) worked on the synthesis of indigo for over twenty years Credit: Science & Society Picture Library
ton, it was widely used, especially for navy-blue uniforms. By the late 19th century nearly all indigo came from indigo bush plantations in India. The German chemist Adolf Baeyer succeeded in making it in the laboratory in 1878, but it took nearly three decades to find a method of making synthetic indigo on a large scale. The breakthrough came in 1890 when Karl Heumann in Zurich found a way of making indigo from aniline. A lucky accident at the German firm BASF involving a broken thermometer then revealed that mercury was a catalyst for a key part of the synthesis and BASF started the production of synthetic indigo in 1897. Johannes Pfleger then discovered a better route to synthetic indigo which was used by BASF’s competitor Hoechst.