What is added to the developer to control oxidation of the developing agent by air?

The addition of a preservative to the developer is crucial for controlling oxidation of the developing agent by air. Developers contain reducing agents that are sensitive to oxygen; when exposed to air, these agents can oxidize, resulting in a decrease in their effectiveness. By incorporating a preservative, the stability and longevity of the developer are enhanced, allowing it to maintain proper functioning throughout the development process.

Preservatives work by reacting with oxygen or by creating an environment that minimizes contact between the developer and air. This helps to preserve the activity of the developing agents, ultimately leading to more consistent and higher-quality film development.

Other substances mentioned, such as restrainers, hardeners, and stabilizers, serve different purposes in the developer solution. Restrainers typically inhibit the activity of the developer in areas that do not need exposure, while hardeners strengthen the emulsion layer to prevent damage during handling. Stabilizers are generally used to maintain solutions in a specific state or pH balance, but they do not directly address oxidation.