Operation method of black and white film

For the preparation before development, first of all, when controlling the temperature of the liquid medicine, put the developing tray containing the liquid medicine into another large tray, pour clean water above 20 degrees Celsius into the large tray, and start development when the liquid temperatures in both trays reach 20 degrees Celsius, so that there is more water in the large tray, and its temperature can be kept relatively stable without stirring. If the indoor temperature is too low, you can put an electric heating rod (about 40W) for fish farming in the big plate, and it would be better if there is one that can automatically control the temperature.

Secondly, after turning off the white light, even if it is not a fluorescent lamp, you have to wait for 2-3 minutes before opening the film. The purpose is not only to wait for the light to go out completely, but to let the operator's eyes have a process of adapting to the darkness. When your eyes get used to it, look around again to see if there is any light leakage in the darkroom. In addition, it is best not to use fluorescent lamps in darkrooms, because the switch is not timely, which is far less convenient than using ordinary incandescent bulbs. Finally, before the end of development, the film density should be observed once or several times with extremely weak green light. This is more reliable than simply calculating the development time to grasp the film density, because most practical operating environments and conditions can not meet the theoretical requirements.

In darkroom work, the author also adopts the method of "one pulling and one loosening". After years of practice, this method is not only practical, but also has four advantages: 1 Easy to master and operate; 2. The film can be prevented from being scratched; 3. 2-3 120 or 135 movies can be played at the same time; 4. Sitting operation and elbow support greatly reduce the degree of fatigue. The operation method of this development is as follows:

When the film passes through clear water, it is rolled into a loose cylinder according to the natural rolling force of the film. The thumb and forefinger (or middle finger) of the right hand hold the axis of the cylinder back and forth perpendicular to itself, so that a short film head is exposed from the lower side of the cylinder, and the left hand holds it, and then immerses it into the developer against the right edge of the developing disk to start timing. After soaking in the potion, keep your right hand still, and slowly pull the title to the left with your left hand. When pulling, it should be noted that one fingertip of each hand should gently touch the bottom of the tray to control the film not to rub the bottom of the tray, and not to be too high from the bottom of the tray to expose the surface of the liquid medicine. When the back of the left hand touches the left edge of the disc, release the left hand and let the film roll back to the right by its natural rolling force (at this time, the film may touch the bottom of the disc, but it will not scratch the film because it only rolls up and does not move). After the film is rewound to the right, the right hand remains motionless, and the left hand still holds another piece of film. After rewinding, it is pulled to the left and then released. Pull loose until the whole piece is pulled out. Then switch to the left hand and pull with the right hand. So the hands are alternately loosened until the development is over.

The same is true for developing two or three films at the same time, but it should be noted that several films must be loosened in turn so that they can be in equal contact with the liquid medicine. The operation should also be accelerated appropriately.

If you nail an 8- 10 cm high T-shaped wooden board on the edge of the table where the developing disk is placed, it will be very stable and labor-saving for you to lean your elbow against it during operation.

The above-mentioned in-tray development method also has some disadvantages, that is, the operator's hands should be in direct contact with the liquid medicine during operation, and for a long time, some people with skin allergies may have reactions, itchy skin and even cracking. Therefore, it is suggested that the operator wear latex gloves used by surgeons when displaying intervertebral discs.