Antifoggants
How and when to add additional anti-haze agents—benzotriazole and potassium iodide—to the developer.
Antiveil agents are substances capable of significantly reducing the fog on photographic materials—their use is particularly justified when processing old, expired materials. In some developers, an anti-fog agent (usually potassium bromide) is already included in the formulation—for example, in “Mikrofen,” ST-1, or ST-2. However, when working with severely expired materials, its effect is often insufficient, and in such cases, benzotriazole, potassium iodide, or a combination of the two is added to the developer. It is important to remember: an excess of anti-fog agent not only reduces the fog but also significantly decreases the photosensitivity of the photographic material.
De-fogging Solution "B" (benzotriazole)
It is a 1% solution of benzotriazole in water and is typically used in conjunction with photo paper developers. It is added to the developer at a rate of 10 to 50 ml per liter of developer—the exact amount is determined experimentally during printing, starting with the minimum and gradually increasing as needed.
The development time of photographic film in a developer containing this additive increases, while its light sensitivity decreases—the exposure must be increased by a factor of 1.2 to 1.5. The resulting image has slightly higher contrast, and the fog effect is significantly reduced. The solution remains stable when stored for several months; it is available in 50- and 100-ml bottles.
"Y" De-fogging Solution (benzotriazole + potassium iodide)
A mixture of two anti-haze agents—benzotriazole and potassium iodide—in a ratio of 1:1.3 per 1,000 parts of water. Together, they are somewhat more effective than benzotriazole alone, but this anti-fogging agent is used exclusively for processing sheet-type photographic materials.
For old, fogged photographic paper, add about 30 ml of anti-fog agent per 1 liter of developer. A developer with this additive works more slowly: the development time for the photographic paper increases by an average of 15–30%, and light sensitivity decreases by 15–25%—the exposure must be increased by the same amount. The anti-fog agent effectively reduces, and often completely removes, the fog.
If the original paper is not too heavily fogged, it is best to use a smaller amount—add the anti-fog agent in small portions of 5–10 ml, making test prints, and stop adding it as soon as the fog disappears. It is not recommended to exceed 50 ml of anti-fogging agent per 1 liter of developer. The solution stores well and retains its properties for at least 6 months.