'Unnatural Colours': An introduction to colouring techniques in silent era movies

'Natural colour' was the term coined for genuine colour photography to separate it from colouring or 'painting' monochrome images, hence the use of the contrasting term 'unnatural'. The intention of this paper is to provide a guide to the technical literature on the subject. It reviews where the technologies originated, the principle literature of the time, and later, that describes the 'recipes', techniques and chemistry, summarizing the image dyes themselves in a database. Additional content is provided from associated technologies such as the subsequent use of the same techniques for natural colour, analogue coloured film restoration techniques, and an excursion into the technological cul-de-sac of Sonochrome.