الأوراق الحساسة .. كتاب التحميض والطبع والتكبير

Chapter Seven
delicate leaves

Photographing operations usually aim at a main goal: to obtain a positive image of the subject that has been photographed, whether this image has the same area as the negative image (i.e. a printing process) or its area is larger than that (i.e. an enlargement process). .

The negative images are printed or enlarged on sensitive paper that is nothing more than a paper support with a positive emulsion layer consisting of gelatin in which light-sensitive silver salts are deposited. The support may also be made of glass, or sometimes celluloid, with a positive sensitive layer on it.

There are two main types of sensitive papers:

(a) Sensitive papers on which a latent image is formed when exposed to light, then it is necessary to treat it chemically to convert the latent image into a visible one. These papers are prevalent in the vast majority of photographic processes, and are known as Development Papers.

(b) Sensitive papers on which a visible image is formed after exposure to light directly, which are known as Day light Paper, and we will talk about them in detail elsewhere in this section.

In general, the characteristics of sensitive papers differ from each other in aspects, as shown after:

First) PhysicalCharacteristics

(a) The color of the paper: some of it is white, while some of it tends to yellow, Ivory, Cream.

(b) The degree of surface growth: some are smooth, others are rough, and third types are embossed.

(c) The degree of glossiness of the paper: some are glossy, others are semi-matt, and a third is completely matte (matt).

(d) Paper thickness: Some sensitive papers are thin, Single Weight, and others are Double Weight.

The choice of the type of sensitive paper suitable for printing or enlarging operations depends to a large extent on individual tastes. This is controlled by factors related to the artistic sense and what the photographer deems appropriate for the subject of the image. Leaves that are slightly yellow (cream) may give the image warmth, so it may be suitable for portraiture or landscapes in which the sun is shining. Papers with a white backing are also suitable for pictures of machines or landscapes in winter and pictures of snow and mountains. Silhouettes or pictures prepared for scientific or research purposes, etc. are also suitable for shooting conditions against light sources.

It is necessary that the photographs prepared for printing purposes be glossy, smooth, and even highly polished, as they are better able to show the finer details of the images, which is a necessary feature when photographic transfer. Reproduction.

Rough, matte paper would hide a great deal of graininess if we wanted to enlarge the image a lot. Sometimes the delicate papers with striking embossed surfaces may be faulted because they attract the attention of the viewer of the picture to the inscriptions on the paper, so the mind is not focused on the photographed subject itself.

Finally, we say that this matter does not have any specific restrictions. Rather, the paper test is subject first and foremost to the photographer's own sense of aesthetic values ​​and what he deems appropriate to perform his purpose.

Second) the difference in its optical properties: Photographic Properties
(a) For the photosensitivity rate.
(b) For the degree of variance,
(C) for its class sensitivity.