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HARDENING BATHS

Increasing the temperature of the solutions in which sensitive films and papers are handled will result in a decrease in the hardness of the gelatin, and the swell may swell or separate from the support. Gelatin also swells in highly alkaline display solutions (such as the case of display with Meritol salt with caustic alkali). In similar cases, it is necessary to work on increasing the hardness of the gelatin, and this is done with solutions known as hardeners. It is used in one of the following ways:
(A) After washing after the show process.
(B) Immediately after the Stop Bath.
(H) To be mixed with the suspension bath, and then the combined solution is called Acid-Hardener, used after showing and prior to fixation.
(k) To be mixed with the settling and suspension bath together, and then the triple bath is called Acid-Fixing-Hardener.
(e) Indeed, some gelatin hardening solutions can be used even prior to the demonstration process.
(f) One of the hardening solutions is what is sometimes used after stabilization operations (in some cinema films).

The following materials are commonly used to increase the hardness of gelatin:

A - Chrome Alum.

2- Potash alum, sometimes known as alum
Potassium Alum.

3- Formaline, and its solution is sometimes known as Formaldehyde

4- Tannic acid, which increases the natural physical hardness by its ability to resist scratches resulting from friction while wrapping it. Tannic acid is not used except after the final fixing and washing operations.

First: Increasing hardness by means of alum chromium:

Chrome Alum is a toxic, easily soluble salt in water that we get in the form of a scarlet powder, or standing violet crystals that look scarlet or red standing when looking at them in interspersed smears. This salt has a great ability to increase the hardness of gelatin. A solution can be made to increase the hardness of the film gelatin immediately after showing by immersing it for five minutes in a solution of para-chromium, concentration (e) (such as Gephardt solution No. 356). And if the weather is hot, you should also work to prevent swelling of the gelatin by adding to the solution an amount of crystalline sodium sulfate (as is the case in Giffart’s solution No. 357, which was prepared to increase the hardness of gelatin in hot weather).

Whether the scrum-like hardening solution was tried independently, or it was mixed with the suspension bath, or mixed with both the fixation and suspension baths together, it can be tested for its suitability for increasing the hardness by looking at it in interspersed rays. It appears green in color, then it is an exhausted solution that is not suitable for use.

And if the alum chrome solution was mixed with other acidic solutions (such as the suspension bath or the acid stabilization bath), it will not be able to perform its function of increasing the hardness except for a few days, and for this reason it is usually recommended to use it within two or three days at most after its preparation.

Likewise, the ability of the semi-chrome solution to perform its function as a solution to increase the hardness decreases if it is mixed with organic acids in particular (such as citric acid or acetic acid), even if the semi-chromium solution is newly formed. For this reason, it is recommended that the film be washed with water after leaving the suspension bath and prior to immersion in a chrome-like hardening solution.

Second: Increasing hardness with alum potash salt:

Potash alum is a salt sometimes known as potassium alum. We get it either in the form of transparent crystals or in the form of a powder. It is stable in properties and does not require special precautions to preserve it. It is easy to dissolve in water, and its solution is acidic, and the speed of its solubility increases in warm water, which does not harm its properties (unlike semi-chromium).

And if the semi-chrome is characterized by its strong ability to increase the hardness, the alum = potash is distinguished by its ability to survive despite the acidity of the solution. Rather, it is required that the = solution be acidic in order to prevent the precipitation of aluminum hydroxide that results from mixing the hardening solution with the alkali residue of the show solution. It is possible to prepare a suitable solution to increase the hardness by mixing a solution of its concentration (2) of semi-potash with two other solutions of sodium sulfate and glacial acetic acid, each of which has a concentration.
Also, we can prepare an acidic solution to increase the hardness of gelatin by means of alum potash to be added to the hypo-fixation solution, and so on. Mixed with one acidic solution for fixation and to increase the hardness of gelatin. Acid-Hardening-Fixing Bath