"Chemigram #17"

gelatin silver chemygram (paint with chemistry on baryta paper)

With the chemigram, developer or fixer is used to paint directly onto the photo paper. This happens in daylight, which is why the photo paper reacts immediately with the respective chemicals. If you paint with developer, the paper immediately turns black, after which it is rinsed briefly, fixed and finally watered. When applying fixer, only a small light colouring of the paper is visible. After an exposure time of about one minute, the paper is placed in the developer tray. The unpainted areas blacken. Afterwards, the paper is watered again, then fixed and finally watered.
(Christoph Fuchs)

The unpainted surfaces blacken. Then watered again, then fixed and finally watered. Johann Schulze is considered the first to produce a chemigram-like image. In 1725, he succeeded in such work using opaque paper and a bottle of silver nitrate. Frenchman Hippolyte Bayard produced another chemigram-like image in 1839 while performing sensitization tests. In the 1930s and 1940s, Edmund Kesting and Frenchman Maurice Tabard made paintings and pictures with developer and fixer on photographic paper. However, it was the Belgian artist Pierre Cordier (b. 1933) who was most significant in the development of chemigrams.
(wikipedia)