حمام الإيقاف stop bath .. كتاب التحميض والطبع والتكبير

Chapter Five

Suspensions, hardening, stabilization, final washing and drying.

Presentation results:
The display process results in the following results:

1- Traces of the apparent solution remain attached to the sensitive gelatinous layer, and should be extracted from it so that the reduction process does not continue.
2- The apparent solution reduces some of the silver salts granules to the exclusion of others, so they remain deposited in the gelatinous layer and are liable to blacken if exposed to light.
3- It is possible that the hardness of gelatin will decrease as a result of its saturation with water or a show solution, especially if the temperature is high. In order to avoid the first result, which is the presence of traces of the apparent solution, the sensitive film or board should be washed with water until these traces are removed, and work should be done to stop the reduction process.

In order to avoid the second result, the silver salts that have not yet been reduced must be removed, so that the image becomes stable in color.
In order to avoid the third result, work must be done to increase the hardening of gelatin.

The following washing process to show:
This is done in a stream of running water whose temperature is close to the temperature of the apparent solution so as not to damage the gelatin layer as a result of the temperature difference, and it is taken into account that the washing period is sufficient to remove the effect of the apparent solution attached to the gelatin. The filtration takes between half a minute and a minute.


STOP BATH

Due to what may happen during washing from the persistence of the effect of the solution appearing on the sensitive layer, therefore it is better to stop the reduction process by means of what is called the stopping solution or by the name of the stopping bath sometimes after dipping the film or the sensitive plate in the water.

We have already mentioned that the apparent solution contains alkaline substances among the materials that it is composed of, and these substances are equivalent to the preservatives if they are acidic in nature, and they increase the alkalinity of the solution to activate the reduction process (because reduction is active in an alkaline medium and stops in an acidic medium), and on It is if we want. Stopping the display (reduction) process. It is easy to do this by placing the film, sensitive board, or backing paper in a very diluted saline solution, so the reduction process stops immediately.

This is not considered a stop bath is necessary in all cases, because the continuation of the reduction for a few seconds during the washing process, does not have a tangible effect if the solution appears to be weak in activity. Especially if we know that the reductive activity decreases a lot once the film is dipped in the washing water.

However, the use of the suspension bath is necessary in the following cases:
(a) If the solution is of high energy developer.
(b) If the apparent solution is very fast (there are enough solutions for five or ten seconds to show the film).
(h) If the temperature is high.

There are acids or substances that stop the process, including citric acid or very diluted acetic acid.

It has been observed that when the alkaline substance in the appearing solution is sodium carbonate, it escalates when carbon dioxide is gassed as a result of the interaction of sodium carbonate with the acid, and the accumulation of these gas bubbles on the surface of the gelatin layer, so they become an obstacle to fixing the film well. Therefore, moving the film several times improves these gas bubbles.

Other substances other than those we mentioned are sometimes used, and their solutions are an acidic medium that stops the reduction process, such as potassium metabisulfite salt. It is taken into account to change the stopping acid if it turns greenish in color or if it has been used for a long time, because then. Due to the reaction of the alkaline show solution with the stopping acid to form a neutral solution.

The stopping process may not take place in a bath of its own, but sometimes it is considered a single acid bath in which the stopping process is carried out with the process of increasing the hardness of the gelatin (Hardener) Stop Bath & Also, the processes of fixation, increasing the hardness of gelatin and stopping may sometimes mix in one solution that brings them together and is then called as Acid Fixing & Hardener, and we will talk about each of the last two cases in this section when we discuss the issues of increasing the hardness and “fixing”.
Sodium sulfate may be added to the stop bath when it is necessary to work at high temperatures, as one of its properties is to prevent swelling of the gelatin in the acid stop bath - Kodak.

Prepare a dilute acetic acid solution:
It is usual that the composition of the suspension solutions requires the preparation of a dilute solution of acetic acid with a concentration of 28%, and it is also usual to obtain acetic acid (commercially) more concentrated than the above. Therefore, we mention in the following how to prepare the diluted solution (28%).

(a) If the acetic acid is glacial (and it sometimes cracks) then add three parts of it to eight parts of water.

(b) If the acid concentration is 80%, then five parts of it are added to nine parts of water.

(h) If the acid concentration is 50%, then one part of it is added to an equal part of water.
Here are examples of the suspension bath installation.