Desensitising refers to the process of reducing the light sensitivity of a photographic emulsion after it has been exposed. This is typically achieved through the application of special dyes or chemical oxidation agents, which make the emulsion less reactive to further light exposure.
In traditional film and darkroom photography, desensitising is particularly useful when handling materials under brighter conditions than would normally be safe, helping to prevent unwanted fogging or degradation of the image. By controlling sensitivity in this way, photographers can maintain greater control over the development process and preserve image quality.