Why are silver compounds used in photography?

Silver is used in film media because it tarnishes better than other materials.

Tarnish is the process of oxidation, where a metal turns from some some shiny color to a darker non-shiny color.

Three Examples of Tarnish:

1. Gold: Starts a bright shiny gold color and tarnishes to a slightly darker dull gold color
2. Copper: Starts a bright shiny orange-gold color and tarnishes to a green patina color
3. Silver: Starts a bright almost white color and tarnishes to a very dark grey, almost black color

Silver provides the best tonal range, from light to dark. It can capture light from pure white to pure black (or very close).

Additionally, silver tarnishes very consistently. This provides a smooth transition from light to dark on film.