Gum Bichromate

The gum bichromate depends on the reaction between dichromate salt mixed with a gum or gelatin. The gum becomes insoluble in water, and after exposure and development, retains the solid pigment particles, while the rest of the dichromate is washed away.

Some of the process is to:

1. Put pea-sized amount of pigment onto your plate and add 5cc of gum and mix together.
2. Add 5cc of saturated dichromate and mix.
3. Tape a piece of paper to a flat surface and mark off an area with pencil to add the negative to. Coat paper with lightly damp brush. 
4. Place in the dark for at least 4 minutes until dry.
5. Place the negative with emulsion side up on the paper. Tape down outside picture area and make two holes through margin of both the negative and the paper.
6. Develop in lukewarm water to wash away insoluble gum.
7. Dry in strong stream of warm air.
8. Recoat using more pigment and repeat steps 1-7.
9. Dry and fix in UV light for a short time. Wash for 6 hours.

https://blog.scienceandmediamuseum.org.uk/introduction-gum-bichromate-printing/

Examples:

https://printedpicture.artgallery.yale.edu/videos/gum-bichromate
https://www.parisphoto.com/en/Glossary/Gum-bichromate-print/