fotobleaches

Fotobleaches, also known as photographic bleaches, are chemical solutions used in photographic processing to remove or lighten developed silver images. This process is a crucial step in certain photographic techniques, particularly those involving reversal processing or the creation of monochrome prints with specific tonal qualities.

The primary function of a fotobleach is to oxidize the metallic silver that forms the image into a soluble silver compound. This silver compound can then be washed away with a subsequent fixing bath, effectively removing or reducing the density of the silver in the emulsion. Different types of fotobleaches exist, each employing various oxidizing agents. Common examples include potassium ferricyanide (often in combination with a bromide salt), potassium dichromate, and persulfates.

Fotobleaches are integral to processes such as the subtractive color reversal process, where the initial color image is formed by dyes, and the silver image is subsequently bleached out. In monochrome printing, bleaching can be used to achieve highlights, reduce overall contrast, or create special effects by selectively removing silver. The effectiveness and selectivity of a fotobleach depend on its chemical composition, concentration, and the duration of its application. Careful control of these parameters is essential for achieving the desired photographic outcome.