The invention of photography dates back to 1825, a technique that was democratized and became accessible to the general public in 1839 with the appearance of the daguerreotype, a positive process for fixing an image.
Thereafter, three media for fixing an image coexist :
- the paper medium, with the production of the first black and white print in 1840, then the arrival of colour in 1862 thanks to the invention of heliochromy.
- the glass support, which appeared in 1847 and spread to a wider public from 1854. Colour was developed on this support from 1891 onwards.
- the cellulosic medium, with the first black and white negative in 1889, then the colour negative from 1939. The positive was created in 1930 with the invention of the slide.
All of these media are particularly sensitive to humidity, but have a good shelf life if kept in a dry place and at low temperatures. The glass plate is particularly fragile and requires a vigorous digitisation policy to avoid manipulation.