الصورة الكامنة Latent Image .. كتاب التحميض والطبع والتكبير

Chapter Three: The process of manifestation

Latent Image

No visible change appears in the film after exposure to light from what it was prior to exposure, but the reality is that there is a latent image that may have formed as a result of the effect of light on the sensitive layer, and this image does not appear unless the sensitive layer is treated with a special chemical method known as “developing” After that, the latent image turns into a negative image. In the colloquial language, the display process is called the “acidification process.” It is, in fact, a process of reducing silver salts that have been affected by light, turning them into black metallic silver deposited in gelatin.

However, during the exposure period, all silver salts deposited in the gelatin of the sensitive layer are not reduced. As only a part of it is reduced, and its percentage may not exceed 25% of the amount of silver salts, so the rest is capable of being reduced if it is exposed to spoilage, then the negative image is destroyed, and then it is necessary to get rid of these excess salts, through a chemical process Another is known as the “fixing process”, and it is in fact a process of “removing” or “dissolving” the silver salts that have not yet been reduced to get rid of them completely, so nothing remains in the sensitive layer except the black metallic silver that is attributed to the black color that we see in the negative image. The film must be washed after each of the two processes of showing and fixing (Fig. 25). Although a definitive opinion has not yet been made about how the underlying image occurs and about the change that occurs to the sensitive layer after exposure to light, there is a modern theory developed to try to explain this, and this theory assumes that when a grain of silver salt is exposed to light, centers of sensitivity known as Sensitivity are formed. specks. In order to comprehend the basis for assuming the presence of sensitivity centers, we mention what we see when the nursing increases very much beyond the amount needed to form the latent image, as then the color of the sensitive layer changes and the image appears visible, not latent, and this is due to decomposition. Silver is divided into two parts, which are bromine and silver, so the silver appears on the surface of the grain in the form of small dots or specks, and this phenomenon we all notice when we put any sensitive film or plate in strong daylight with a small object on it (such as a key, for example), as we see at that time that a visible image of the key has formed. After a period of time has elapsed since the raw film was exposed to light, hence the thought arose that the latent image is nothing more than a collection. Small dots of metallic silver are formed on the surface of silver salts crystals when the photosensitive film is exposed to light. The size of the sensitivity centers in a silver bromide pellet does not exceed one hundred millionth of the size of the pellet itself.

The occurrence of the latent form is explained by the fact that silver atoms are naturally dispersed in a silver halide grain (Fig. 1-26), and the latent form requires that a number of silver atoms gather together for its formation. This is done when light rays fall on the particle (Fig. 26-), and these atoms gather to form a center of sensitivity (Fig. 26-h). The process of collecting silver atoms is similar to the formation of the sensitivity center, the process of collecting water droplets to form fog or rain, or the process of collecting dissolved salts in spheres to form large crystals.
It is thought that the apparent solution, when it begins its work, attacks the grain of silver salt, starting from the “center of sensitivity”, so that its crystals dissolve into its two halves, and they appear in a black color that is the color of raw metallic silver, and thus the latent image turns into a visible image. This theory (1) also assumes that the duration of exposure and the amount of light energy are the centers of sensitivity. If the light energy increases with the duration of exposure decreased (as is the case with electronic flash photography), the number of sensitivity centers increases and their size decreases. Conversely, these centers increase in size and decrease in number. If the duration of exposure to light is long and its quantity is reduced (Fig. 27). Based on the previous assumption, it explains the reason for the necessity of increasing the exposure time in the case of shooting with flash light than in the case of shooting with ordinary tungsten lamps. It is amazing what was mentioned (3) about the extent of the ability of this latent image to survive, despite the passage of a very long period between exposing it to light and showing it. It happened that an exploration expedition to the North Pole took place in 1897) and photographic images were recorded at that time, and then this expedition was destroyed at the pole. North in that year, and was found on the side of its members in . 1930, along with what they were carrying of important supplies, photos and sensitive plates that had not yet been shown, and by showing them it became possible to obtain from them a very acceptable photographic machine, despite the passage of 33 years between photography and display.