الاظهار بالاسفنج ١-a .. كتاب التحميض والطبع والتكبير

Sponge development Sponge display

When it is required to show large areas of sensitive paper to cover a wall, for example, with one photographic image, it may not be possible to perform the demonstration operations in a basin suitable for the size of the paper, and then a sponge is saturated with an amount of display solution and moved quickly and regularly over the surface of the sensitive paper so that every part of it is treated equally.

Safe light suitable for showing films:

Although it will not be possible for the trained photographer to perform the projection operations in a completely dark room, it is also permissible for him to use light sources with specific colors and spectral characteristics that facilitate his work when showing films. These light sources are usually known as “safety light.”
The safety light may be a large white lamp with colored glass in certain colors, or it may be a sealed box with a white lamp inside, with one side of the box equipped to place a colored glass, which is in fact a light filter that does not allow certain rays to pass through it, provided that these rays do not respond to the film that It will be shown (that is, provided that science is not affected by these rays). The color and characteristics of the appropriate safety light for each type of sensitive films or papers depend on that property known as “spectral sensitivity” that is characteristic of sensitive films and papers, and indicates their sensitivity to colours. Some films, for example, are not affected by red colors (such as orthochrome and matic films), and therefore it is permissible to show them in a dark red safety light, and others are affected by all colors of visible rays (such as brown and matic films), and therefore they must be shown in complete darkness.
For the tenth Maha in safety, the Emirate, the work was about 130 cm, although the lighting was indirect and was prepared so that it would be reflected by Duane and whether it was condemned
The power of the light source depends on the purpose for which the safety light was prepared. For example, the power of the lamp intended for showing panchromatic films differs from that used for showing chloride papers. The strength of the light source also depends on the method that will be followed in the lighting, as it is either direct lighting (Fig. If the lighting is direct, a lamp of (10 watts) is sufficient, provided that its distance is not less than the light table on a reflective surface (Fig. If the distance is increased to cm, as if the ceiling is high, or the lamp is directed towards a far wall, a lamp with a power of approximately 25 watts may suffice.
In general, it can be said that it is required for a safety light lamp that its strength does not exceed the limit needed to help the human eye see in the dark after it has acclimatised and prepared to see in this low light level. It is advisable to prepare in the box a way to ventilate it whenever possible, as the spectral characteristics of the filter may change when the temperature exceeds a certain amount. This condition can be overlooked if the lamp is weak so that it does not cause its temperature to rise too much.
In order for the photographer to always be on the safe side, it is more appropriate for him to obtain the lamps that he uses from a store that sells photographic equipment, and not from a regular electrical store. The wisdom in this is that the rays that come out from the light source may contain other unwanted rays of light and the sensitive layer responds to them, which results in its damage. Certain sensitive film or paper. Since we have seen the close connection between the color of the safety light and the spectral sensitivity in the films, this is why it is important for us to know it. Films are divided according to their spectral sensitivity as follows:

A - Blue Sensitive Films:
Sometimes known as color blind or process films. As indicated by its name, it is affected by blue and violet rays, just as it is affected by invisible ultraviolet rays. Accordingly, these films can be shown in dark red, dark yellow, dark orange, dark olive green, or brown safety light.

B - Orthochromatic films, which are affected by all visible rays except for belt rays, and therefore they can be shown in a standing red safety light.