This paper aims to show, from the case study of the Swiss professional photographer Gaston de Jongh, that the 1930s were a pivotal period in the history of colour photography, during which scientists, photographers, and printers were working closely in the search for a high quality and accessible colour process, at a time when, between the Autochrome and the Kodachrome eras, no process seemed to establish itself permanently. This process must then meet the overriding criterion of printed reproduction, since advertising was one of the main drivers of this technical advancement.