Silver Halide
The Chemistry Behind Photography

Silver halide has been the cornerstone of photography for over a century, capturing our world in stunning detail. But what exactly is this light-sensitive material, and how does it translate light into a lasting image?

 Silver halide is a class of chemical compounds formed between silver (Ag) and a halogen element, like chlorine (Cl), bromine (Br), or iodine (I). The most common types used in photography are silver bromide (AgBr) and silver iodide (AgI). These tiny crystals are suspended in a gelatin coating on photographic film or paper, creating a light-sensitive emulsion.

The magic of silver halide lies in its light sensitivity. When light strikes a silver halide crystal, it disrupts the arrangement of electrons, creating a "seed" for the formation of metallic silver. This initial change is invisible and is called a latent image.

Capturing this invisible image requires a development process. When the exposed film or paper is dipped in a developer solution, the silver halide grains with the latent image are preferentially converted to metallic silver. These areas become dark, while unexposed areas remain unchanged. The film is then fixed in a solution that removes the remaining light-sensitive silver halides, making the image permanent.

The size and distribution of the silver halide crystals play a crucial role in image quality. Smaller crystals produce finer detail, while larger crystals produce grainy images. Additionally, different silver halides have varying sensitivities to light. Silver iodide, for instance, is more sensitive to blue light, making it useful in colour photography.