Summary Peter Griess synthesized the first diazo compounds in 1858. August Kekulé played a key role in the elucidation of the structure of this new class of compounds. Around 1886, the photosensitivity of diazo compounds was discovered. This was used to develop the diazotype, a silver‐free copying process which produces azo dyes. Finally, a suggestion is made on how the diazotype can be implemented in chemistry classes.