نظرية التثبيت .. كتاب التصوير علم وفن

Fixing theory: Fixing

Fixation means the process of removing the silver halogens that were not exposed to light, as well as those that were not reduced, and thus fixing the film. This can be done by dissolving silver halogens in a solution of a substance in which silver salts are soluble. There are many materials, the best of which is sodium thiosulfate, or what photographers call “Hypo”.

And the silver halogens dissolve in the thiosulfate solution to form a series of silver thiosulfate salts that dissolve in water. The disadvantage of using thiosulfate alone is that the developer is still working inside the film, and therefore it is preferable to add acid to stop the reaction of the developer. But the presence of acid with thiosulfate leads to precipitation of sulfur, and this can be avoided by using sodium bisulfite instead of acid. The fixing solution is as follows:

Sodium thiosulfate (Sodium Metabisulfite) Sodium Bisulfite Sodium Water

200 gr

gram

,1000 cm

After that, it remains to wash well with water to remove any silver salts that may affect the image in the long run. .

Thus, the negative image appears on the film, where all degrees of shades from white through gray to black appear reversed, so white in reality appears black and so on.. Therefore, it is necessary to reprint the negative on sensitive paper to obtain the positive image, where white appears as white, black as black, and gray degrees according to their natural gradation. .
zoom.

In order to obtain images larger than the size of the negative, it is necessary to do the so-called |

It is noted that there are three things that affect the quality of the acidification process, and a fourth that affects the acidification process

All shoots:

- Composition of solutions

Temperature - - Acidification time 4 - Complete cleanliness and order

Therefore, it is necessary to take into account:

1- Adhere to the instructions of the film producer.

2- Use a good thermometer, intended for good temporary use, intended for use in the dark room for photography.

- Complete cleanliness and order

Magnification: This is done through a magnifying device (which is the most expensive device in the dark room, by the way) where the sensitive paper is exposed to the light that passes through the negative and then the lens of the magnifier until it falls on the sensitive paper placed on the base of the magnifier and when sufficient exposure is done (appropriate lens aperture + enough time) With the help of a timer, we start the process of developing sensitive paper to obtain a positive image, and all of the above is done in complete darkness or under the safety light of developing sensitive paper in black and white (in complete darkness or under

safety light):

1- Insert the sensitive paper (which was previously exposed under the magnifier) ​​gently under the exposure solution.

2- Gently shake the basin containing the highlighter solution until the image appears completely (at a specific temperature for a specific time according to the instructions of the paper manufacturer sensitive).
4 Transfer the sensitive paper to a basin of washing water or a stopping solution (an acid solution to stop the de-priming process). Transfer the sensitive paper to the mounting tray (then the room can be lit) and leave it for five minutes, agitating it occasionally.

E - Wash in running water for at least half an hour. 6 - Hang the delicate leaves in a dry place away from dust.

Sensitive paper development steps
Developing colored sensitive films and papers:

In fact, these processes are like black and white developing, but they are more complex and require extreme accuracy in timing and keeping the temperature within degrees Celsius. This is a thorny topic, so you should confirm the references or wait for our next book on acidification, printing and enlargement, God willing