الاظهار على مرحلتين في محلولين منفصلين .. كتاب التحميض والطبع والتكبير

Display in two phases in two separate solutions
TWO-BATH DEVELOPMENT

The display process is carried out in this way in two solutions and in two stages:
1) The first stage
The first solution carries the reducing agent, such as metol and hydroquinone, along with the preservative (such as sodium sulfite). Since this solution does not contain alkaline substances to activate the reduction process, therefore, it is not expected that the process of showing will start when the film is placed in this solution. If light traces of the image appear at this stage, this is due to the weak alkalinity that characterizes sodium sulfite. Therefore, sometimes an amount of cane sugar and sodium bisulfite is added to the first solution, so that the appearance of the image is delayed at this stage. We conclude from the foregoing that this stage is limited to completely saturating the film with the first solution, without any chemical reaction taking place.

There is no doubt that it has now become clear that this solution will not deteriorate in any way, no matter how long it is used, because there is no interaction between the silver bromide (which is deposited in the sensitive layer) and the reducing agents (in the solution). Thus, the properties of this solution remain constant, and therefore there is no need to increase the duration of exposure if the number of films that are treated in this solution is increased, and the degree of contrast in the films remains completely constant, whether the film that was treated in this solution is the first film or the last film, as long as The period that each film can hold in the solution is equal to the period that the other film can hold, and the increase in the number of films only results in a decrease in the amount of the solution as a result of the saturation of the films with it, unlike the usual display solutions with one solution that are exhausted by the large number of films in which they are shown and quickly spoil. This calls for us to increase the duration of showing each film compared to the previous one, or adding new solutions to activate the Replenishers after showing a certain number of films, otherwise the last films appear to be underdeveloped or deficient in contrast. 9 Soft than before.

2) The second stage

As for the second solution, it contains activated alkaline substances, without which it would not have been possible to reduce silver bromide to metallic silver. When the film moves to the second solution, it is saturated with the first solution, and accordingly the reduction process begins as soon as the film is dipped in this second solution, so the complete reaction will be rapid. And since the second solution contains only alkaline substances - which are cheap materials in Yemen - and given the susceptibility of this solution to rapid deterioration (since the actual chemical reaction takes place in it, and the products of the reduction process are mixed with it), therefore it is not harmful to replace it with a new solution whenever it becomes depleted. After using it to show a certain number of films.

Summary of advantages of bi-solution embossing
(a) Lower costs, especially if we make the quantity of the second alkaline solution small, so that it is only sufficient to show one movie, or a limited number of movies.
(b) The stability and equality of the contrast and density degrees, whether this film. The first in the order of display or was the last (assuming that the alkaline solution was changed at the appropriate time).
(h) The two-stage display process is often used as a means of rapid display (please refer to p. 161). The following are examples of the installation of two-phase solutions.