العوامل التي تؤثر تأثيرا سيئا في الطبقة الحساسة .. كتاب التحميض والطبع والتكبير

Factors that adversely affect the sensitive layer:

(a) Moisture:
Gelatin has the ability to absorb water vapor. This may be
The unit of education, the violin, is the absorption in an inconsistent degree, so spots appear on the negative image after showing it. Some manufacturers of photographic materials wrap their products with moisture-resistant covers designed for hot areas, and if these covers are not completely sealed, these products are damaged by moisture: and with an increase in caution, it is better to put some materials that absorb the vapor of substances that contain water in the storage places for sensitive materials, such as Calcium chloride chloride or dried rice if the storage is in a wide place.
(b) the length of storage period:
If the sensitive materials are stored for a long time after their manufacture, the silver salts granules become capable of being reduced by the apparent solution despite not being exposed to light, so the clarity of the negative image becomes less clear and it becomes covered with a gray color.
It is possible to add some chemical compounds to the show solution to fix the defect resulting from the long storage. Perhaps the best place to store for an appropriate time is the cool dry place.

(H) Chemical fumes: Sensitive layers are affected by fumes and gases, which leads to the formation of what is called chemical fog. Examples of these gases are: carbonic gases resulting from the combustion of turpentine or oils, gases that result from chemical reactions, and fumes of some substances.

(5) Light fog: This defect results from the arrival of any amount of light to sensitive materials, either directly or as a result of not wrapping them tightly after use, or as a result of placing them in intense light while they are wrapped. The thickness of the sensitive layer:

The thickness of the sensitive layer varies according to the purpose for which it was prepared. Films with a thick sensitive layer increase the amount of silver salts, so their density increases as a result of the development process at a faster rate than those with a thin layer. However, the latter, in turn, is characterized by an increase in sharpness of the image in it compared to that in the thick layer, as the Irrediation decreases as the sensitive layer thins, which increases the sharpness of the image. In an explanation of what we mean by “light diffusion”, we mention that when the light rays fall on the sensitive layer, they spread in it as a result of their reflection on the crystals of silver salts (Fig. It negatively affects the sharpness of the image after showing it, as the light point emanating from the object becomes, accordingly, an indefinite light spot (Fig. 3). The amplitude of the dorsal diffusion increases with the increase in the thickness of the sensitive layer (Fig. 4). as

It also increases whenever the exposure time is more than the appropriate limit, and this is self-evident as it follows Increasing the light energy increases its ability to reach deeper parts of the sensitive layer, so that silver salts crystals in areas that were not directly exposed to light become capable of being reduced during the acidification process.
Covering sensitive gelatin with a more solid layer: Over coating

It is a means intended to protect the thin layer of gelatin from scratches that may result from wrapping films or otherwise. It also protects it from the adhesion of any sediment likely to be attached to the presenting or fixative solution. It also prevents possible scratches on the surface of the gelatin as a result of its friction with the basins during the displaying operations.

Covering the backing: Film Backing

When the film is placed in the presenting solution, the gelatin layer swells to a slight degree, then expands as a result of its saturation with it, and after the completion of the display processes and the start of drying the film, the gelatin layer retracts from what it was first, while the support remains as it is without the liquids having any effect on it, which leads to a curvature The film backing is inward if it is made of celluloid. In order to overcome this situation, a very thin layer of gelatin is sometimes placed behind the support on the other side of the sensitive layer, and the shrinkage coefficient in it is equal to the coefficient of shrinkage of the upper sensitive layer, so the degree of shrinkage of the two surfaces is equal and the support remains flat.

Films with two layers of different sensitivity: Double Coated Emulsions

Some films are made to be covered with two layers of different sensitivity that are placed on the film support, in order to overcome the defects that result from overexposure. The upper layer is sensitive to light and the lower layer is less sensitive. If the duration of exposure to light exceeds the required amount, the upper sensitive layer is affected, while the lower layer resists this error and is affected only to a very small degree due to its low sensitivity. Thus, the negative image is acceptable and of medium density. In this way, too, it is possible to overcome the underexposure deficiency, as the fast-sensitive upper layer is sufficient to record the latent image in the event of insufficient light.