How did photographers in the past post-process photos?

When developing film, many factors such as contrast, gradation and grain can be controlled by the concentration and temperature of chemical solution, development time and motion amplitude. When printing photos, you can also make a fuss about the illumination, time and fixing time of the magnifying glass, as well as various means such as shielding and cutting. The effect is much more natural than modern PS, and that is the real art of light and shadow.