Storage of color materials in tropical conditions.
It is extremely important to maintain appropriate storage conditions in a tropical climate. Hot, dry climate, which prevails, for example. in Egypt or Arabia, it is not so dangerous for the footage. Colored photosensitive materials, intended for longer storage, should be stored in low temperature places, np. in refrigerators generally available in larger centres, from where these materials are downloaded only for direct use. In some countries, it may be necessary to moisten photosensitive materials, because as a result of drying, the tape becomes too brittle and can break when it is moved in the camera. moisturizing, if it's intentional, should be carried out by carefully placing damp paper or damp cloth into a tin box, where the film or tape is stored.
Development is very difficult in tropical conditions, and sometimes even impossible, if we do not have water at a sufficiently low temperature. Black and white materials can be processed by using the so-called. tropical calling. It's about that, that strong tanning agents are added to the solution, which prevent the gelatin from swelling. So far, we cannot apply this to colored materials, because there is a concern about the influence of the tanning agent on the properties of the three color photographic emulsions. If we are unable to develop colored materials on site, test shots should be developed, to check the correct exposure. For this purpose, it is recommended to prepare two sets of exposed samples of colored negative material exposed for approx. V50 sec at aperture 6. One of them must be developed in a color developer, and the other in black and white, np. according to Agfa or ORWO prescription no 16 or Agfa or ORWO no 55.
We take test tapes and some developer with us on the go and can develop samples of color materials in a black and white developer, and then compare them visually with previously exposed samples and check, whether the exposure of the color film under the new conditions is correct. Unfortunately, reversible materials are not suitable for such comparisons, because they have a black anti-reflection layer. Critical storage conditions occur in tropical countries in the case of high temperatures and increased air humidity. Special precautions must then be taken. That is why all manufacturers pack colored photosensitive materials in sealed tin boxes or metal foil packaging.
Wolfen-based ORWO packs colored roll films in tin boxes with screw lids and rubber seals. 35mm films are packed in airtight boxes additionally sealed with a rubberized adhesive. Moisture from the environment cannot get into such packaging and the films should be protected only from high temperatures. Boxes with cinematographic films are double-sealed with insulating tape.
For scientific expeditions, colored materials can be packed into special boxes. The company ORWO from Wolfen prepares wooden boxes impregnated with a preparation against termites for this purpose, lined inside with zinc sheet, which is soldered on the edges. Small boxes are equipped with manual handles,_ so that they can be transported by one porter. They can be shipped by plane or refrigerated ships, relatively by rail.
Be careful when transporting by car,, that the packaging is not exposed to direct sunlight. If conditions allow, refrigerators should be used for both storage, as well as for longer transport of colored materials. However, the cooled films cannot be immediately removed and inserted into the camera, because water vapor from the environment will then condense on the cold membrane, which in turn can lead to sticking of the materials. The temperature of the films and films should be equal to the ambient temperature even then, when they are tightly packed. After removing from the protective packaging, the film should be protected as much as possible from the influence of high ambient humidity. Small exposed amateur loads can be stored in tightly closed jars, np. Weck type, containing silica gel bags or, as a last resort, dry tea or dry rice. The most practical to use is blue silica gel, which is already in the boxes intended for scientific expeditions. The indicator dye contained in the silica gel changes its color from blue to pink as it absorbs moisture. We recognize it immediately, that the gel has already lost its moisture-absorbing properties. By heating it to 120°C, we can regenerate it and remove moisture from it.
Exposed films and films should be sent for development immediately if possible. However, we should inform ourselves beforehand, can we do it, because in some countries it is forbidden to send exposed films and films abroad.
That is some consolation, that colored materials withstand harsh tropical conditions even without special precautions. This fact proves it, that e.g. z 400 photos taken in Java on Agfacolor Ultra T color negative film, at temp. 25-37°C in the shade and with very high humidity, 40% the photos were absolutely flawless, a 30% it had only slight color distortions.