نتائج توالی استعمال محلول التثبيت ١-a .. كتاب التحميض والطبع والتكبير

Results of consecutive use of the fixing solution:

As a result of the successive use of the fixing solution, the following changes occur.

(a) To increase the percentage of dissolved silver in the solution:

(b) The acidity of the fixing bath should be reduced, as a result of the effects of the alkali of the show solutions attached to the films. This is unless there is a Stop Bath between the processes of showing and fixing.

(h) Noting that the negative sensitive layers should carry small amounts of silver iodide (with silver bromide). Therefore, the frequent use of the fixation solution results in an increase in the percentage of apodide in it as well.

(D) The degree of concentration of free thiosulphate ions decreases as a result of the dissolution and reaction of hypo (sodium thiosulfate) with excess silver salts deposited in gelatin.

As a result of these previous results, the fixation solution becomes exhausted and its activity decreases a lot, which is dangerous and affects the ability of the image to remain without damage for a long time:

Therefore, simply increasing the amount of Hypo in the fixation solution is not sufficient to regenerate its activity if it has been exhausted. There are other consequences and damages that cannot be eliminated by simply increasing the Hypo, including the presence of an amount of silver dissolved in the solution, and the presence of iodide in the solution would cause It leads to the following damages:

(a) It reacts with silver bromide, which is deposited in the gelatinous layer of the films that are being fixed, and turns into silver iodide, which is a salt that does not dissolve in hypo at the same speed as silver bromide.

(b) Spots appear on the negative.

There are two ways to follow then:
1- If the quantity of the fixing solution is small (as is the case with most amateurs and small laboratories), then it does not matter much that we throw it away and replace it with a new solution that guarantees the preservation of the image.

2- But if the quantity of the solution is large, as is usual in many movie development factories (for example), then it is not economical to follow the first method, rather one of two methods should be followed:

(a) Either to renew the activity of the solution while adopting other means to get rid of the harmful effects mentioned above.

(b) that the silver dissolved in the fixing solution be re-collected, rather than thrown away; Because silver is a precious metal.