الورق الحساس .. كتاب فن التحميض والطبع والتكبير

Chapter Three Sensitive Paper

There are many types of sensitive paper that can be used to print or enlarge images, and there are three main types: 1 - black and white sensitive papers

from the movie.

- Sensitive colored papers for enlarging colored negatives - Reversal colored sensitive papers for enlarging colored slides: We will not talk about this type in this book, but in a forthcoming book, God willing, the art of reversal. on

First: black and white sensitive paper

B/W Photographic Paper

This sensitive paper is composed of a paper base or support with a layer of gelatin suspended in which silver halide salts (chloride or bromide (silver) are suspended, and sometimes silver iodide is added).

Regardless of the brand of sensitive paper, we can practically divide sensitive paper according to the following specifications:

1- Speed: here is slow sensitive paper made of silver chloride, fast paper made of silver bromide to which some silver iodide may be added, and medium sensitive paper made of chloro-bromide paper.
Adhesive printing. Bromide paper is used for magnification, while chloropyramide paper can be used in both cases.

The companies producing sensitive paper did not agree to make standard speeds for it, such as films. It does not have ASA or ISO speeds, but the most that can be said is that this is fast, slow, or medium paper. The exposure time is known as the experiment. what happened with

2- Contrast gradation:

Sensitive paper is made with different shades of contrast (contrast is the difference between the lightest color and the darkest color in an image). There is soft paper with low contrast (there is no true black or white color (real), to normal paper with medium contrast (black and white and different shades of gray), to hard paper and high contrast (black and white and one or two shades of gray). Just ) .

If we print or enlarge a medium-contrast negative on normal-contrast sensitive paper, we will find that the resulting image on sensitive paper is medium-contrast. If we printed the same negative on soft paper, we would find that the contrast decreased and the image became gray without white or black. If we printed the same negative on hard paper, we would find that the image is high in contrast, mostly black and white. Thus, by choosing paper of a suitable degree of contrast, we can obtain an image with a good degree of contrast from a negative with low, high or medium contrast. For example, a negative with low contrast, from which we can obtain an image with medium contrast by using very sensitive paper (hard) with high contrast.

The producing companies determine the gradation of sensitive paper contrast in numbers. Number 15) means soft sensitive paper with low contrast, and number (2) means normal sensitive paper with medium contrast, then the contrast increases to number (3), (4) and (5), which we find very contrast
There are types of papers with variable contrast paper, whose contrast does not change during enlargement by using different filters, and the advantage of this type is that we only need one type of paper to get any contrast we want from it, except for type No. (5) which is highly contrasted.

N This surface makes the photosensitive paper with different surface textures and shapes. There is a glossy or glossy surface, which is the most capable type to show the fine details of the image, as well as the color appears bright white and black is very black. It is preferable to use it when you want to print these images for magazines and books. In order to show the beauty of this polished surface, it must be polished on a Ferrotyped polishing device, but paper made on a resin-coated base does not need polishing, and this is the most common type these days.

Surface or texture:

The matte or semi-matt surface is preferred to enlarge the pictures that will be displayed in exhibitions or placed in a frame on the wall, due to the lack of light reflection of this paper. Also, this surface may hide grains or fine imperfections that may appear clearly on a polished surface. Some companies may give special names to such surfaces as Pearl or Silk.

Na

Base or pillar

It has already been mentioned that sensitive paper is made of a sensitive gelatin layer on a paper backing. This support is usually made with two thicknesses or two thicknesses: thin (single weight) and symbolized by .., or thick (double weight) and symbolized by it. . . The thin type is preferred ... for pictures that will be pasted on cardboard or will be placed in a frame. The thick D.W type is preferred for large images that will not be stuck on cardboard or will be circulated by hands a lot. And we find that the kind kind
. Cheaper, washes and dries quickly, easier to stick and saves space to store.

There is another type of sensitive paper, which is widespread now, and it is the paper covered with a resin-coated material and is symbolized by the letters “R.C.” This resin prevents the penetration of solutions into the paper and thus consumes less solutions and is easier to wash. It also has a greater ability to survive and spoil this paper if it is polished on Polishing device, in fact, the polished type does not need polishing. from him

Color:

Most of the sensitive leaves are white, but there are some companies that produce ivory or yellow leaves.

6 - Sensitivity to colors: Most of the sensitive leaves (black and white) are sensitive to blue light, to some extent to green light, and blind to red. Therefore, it can be printed and developed in an orange or red safety light, and its position under the magnifier can be adjusted using the red filter on the magnifier.

As for papers with variable contrast, we find two layers in it, one of which is sensitive to blue and violet and has low contrast, and the other is sensitive to yellow and green and has high contrast. And we choose the contrast we want using blue, green and yellow filters

And if we try to enlarge a colored negative on normal black and white sensitive paper (sensitive to blue rays only), we will find that the blue colors in the negative (yellow in fact) look very present, while the yellow colors in the negative (blue in fact) look very light and so we get an image unnatural .

Some companies, such as Kodak, have produced Panchromatic color-sensitive paper by which colored negatives can be enlarged on black and white paper. The name of the paper produced by Kodak is Panalure, and there is only one medium variation equivalent to No. (2). This paper is magnified in complete darkness or under a very faint amber safety light. It has filter No. 10 10.NO.

How to buy sensitive paper?

In order to order sensitive paper of a certain type, you must specify the name of the manufacturer or producer, the trade name of the paper, the type of base, the number of the contrast gradation, the type and color of the surface, the thickness or weight of the paper, as well as the size or size of the paper.

Example :

Manufacturer name: Kodak.

Paper name and base type. Kodabramide.C. Paper size or size 8X10 inch.

2.Normal paper contrast (NO.

The surface is glossy.

Paper color white.

sheet thickness d. W.

You will find this information written on the box or envelope that contains the sensitive paper, in addition to the name of the display solution suggested by the manufacturer. It is noted that sensitive paper is sold in a box or envelope made of cardboard, and inside it are sensitive papers wrapped in black or metallic paper that is not permeable to light. It is preferable to keep the paper in a cool dry place. And if you want to save the paper for a long time, it is preferable to put it in the refrigerator at a temperature of about 4 m. And about taking out the paper, do not open the box for at least 4 hours. until it gains a temperature
The room, so that the cold air vapor does not condense on the paper and spoil it. Make sure when purchasing the expiration date for use.