حمام إيقاف التفاعل The Stop Bath .. كتاب فن التصوير الفوتوغرافي

The Stop Bath

A reaction stop bath is used for the film between the two processes of endorsement and fixing, by using plain water or a mild acid solution. This process has two functions: stopping the display process, and washing off most of the display material suspended on the film, which spoils the fixative solution. It is preferable to use plain water for the bath for normal visible solutions. As for the rapid clarifying solutions, a bath consisting of a mixture of water and acetic acid at a ratio of one part of the acid, degree 28%, to 50 parts of water, is used.

The Fixing Bath

After endorsing the film, all the silver bromide that was not exposed during the imaging process remains on it. Unless these salts are removed, they will darken when exposed to normal light later. Therefore, to fix the image on the crystal, these salts (silver bromide) must be removed by dissolving them in a compound solution of the following:

1 - Fixing Agent
2- Acid
3 - Sodium Sulfite
4- Hardener accelerator
E - Anti - Sludging Agent

1 - Installer

It is the chemical substance that dissolves silver bromide, usually undissolved sodium hyposulfate, and ammonium thiosulfate is also used as a solvent for bromide in rapid fixing solutions.

2- Acid

When we transfer the film from the endorsement solution to the fixation bath, some of the appearance remains on it, even if the film is washed. Some of the endorsement solution gradually oxidizes and turns black, coloring the fixing solution and making it unusable. By adding acid to the stabilizer, this neutralizes the substance's alkalinity in appearance and prevents it from turning black. And fulfills this purpose any kind of acid or acid. Acetic acid is usually used in the fixing solution, as well as citric acid in the fixing solutions in powder form.

3 - Sodium sulfite

Adding an acid to the solution destroys the two stabilizers, sodium hyposulfite and ammonium thiosulfite, unless protection is provided for them by means of sodium sulfite. If this material is added first, it prevents the acid from attacking the stabilizer. All fixing solutions contain sodium sulfate or its equivalent.

4- Solidification accelerator

The gelatinous or gelatinous substance in the sensitive film becomes soft and fragile when it leaves the endorsement process, so we add a hardener or hardener to the fixative to strengthen it during the fixation process. This substance is potassium alum.

5- Anti-Sludging Agent

If the solution appears to be highly alkaline, the potassium alum separates from it in the form of a slurry precipitate and spoils it. Boric acid is used as an anti-sludge agent to prolong the life of the stabilizer.