إظهار الأفلام في درجات الحرارة المرتفعة .. كتاب التحميض والطبع والتكبير

Show films at elevated temperatures

We knew before that there is a maximum temperature at which films may be shown, as the gelatin layer swells and weakens, and it is also possible for wrinkles to wrinkle or separate from the support of the film, if display is done at high temperatures.
However, there are cases in which it may not be possible to reduce the temperature of the appearance, such as the case of the photojournalist, or the researcher who works in the desert in summer, or in tropical areas and does not have the means to adjust the temperature, and his work requires him to verify the results he records in the same place where he works. Therefore, show solutions were prepared.
Especially working at high temperatures known as Tropical Developers. Under this designation, all solutions containing chemical compounds that prevent multiplying or swelling of the gelatin layer at relatively high temperatures are included. And since the increase in the alkalinity of the display solution leads to the activation of the reduction process, so the speed of manifesting increases, and the speed of swelling of the gelatin also increases, therefore. It turns out that the solutions that are able to reduce the swelling of gelatin are those in which the degree of alkalinity is greatly reduced, and some may think that adding formaldehyde to the solution helps to increase the hardness of gelatin. In response, she says: Although formalin has the ability to actually increase the hardness of gelatin in normal conditions, in this case it reacts with sodium sulfite salt. Sulphite and result in caustic soda
The degree of alkalinity increases in the apparent solution, which is an undesirable result. It has been shown that some chemicals, such as Sodium sulfate. Sulphate has the ability to reduce the degree of swelling of gelatin when the temperature of the solution rises, na formalin, and therefore this salt is usually added to the composition of display solutions suitable for working in hot regions.
After the end of the display process at high temperatures, the hardness of the gelatin should be increased - directly - with one of the solutions that lead to this purpose (hardeners). The hardness is increased according to the following:
(a) Either the hardness is increased in a special solution, immediately after showing and prior to fixation. (An example of this is 4- Kodak Hardening Bath, and its composition will be explained in the next chapter).

(b) To mix the hardening solution and the alum solution together in one solution. In the following, we show the composition of some highlighting solutions suitable for working at high temperatures.