The first discovered synthetic dyes, Mauveine and Fuchsine, both named after the colour of flowers, were produced by British and French manufacturers. These new products were among the great sensations of the Great Exhibition in London in 1862. Two years after these discoveries, the azo dyes were introduced by Johann Peter Griess. Griess worked at the chemistry department at the German University of Marburg, led by Adolph Wilhelm Hermann Kolbe. In 1858, he discovered the diazo coupling reaction. Griess found that when an aromatic amine is treated with nitrous acid at low temperatures, an unstable diazonium salt is obtained. Next, the diazonium salt reacts with aromatic amines, phenols, naphthols or pyrazolones to give coloured azo products. Azo dyes are characterised by the presence of a double nitrogen group and represent the largest synthetic dye class. The development of azo dyes started slowly with the so-called ABC dyes. The first azo dye was Aniline yellow in 1859, followed by the first commercially successful azo dye Bismarck brown in 1863. Between the discovery of Bismarck brown and the next useful azo dye lies a period of 12 years, namely Chrysoidine. The breakthrough came in 1875 and led to the systematic start of the production of azo dyes with the Orangés. The dye chemists feared that the range of the azo dyes was limited to yellow and orange colours, but in 1877 Fast red A was the first useful red azo dye. Soon a series of analogue compounds of this dye class was produced, such as the Ponceaus, Congo red and Benzopurpurine 4B.