Black and white photographic paper

Black and white paper is used to write black and white. It can be divided into contact photographic paper (slow sensitive photographic paper) and enlarged photographic paper (chlorine silver bromide photographic paper and silver bromide photographic paper). Depending on the contrast. Classify hard tones, intermediate tones, etc. Photographic pap with a smooth surface is usually used. Large-scale amplification, semi-gloss paper (also with grain surface and silk surface), and sub-gloss printing paper according to the purpose. On the paper thickness, there are thinner, thicker, medium thick and extremely thin (for copying). In terms of size, in addition to the 6*4 inches used by amateur photographers, there are also large specifications for exhibitions, such as whole paper and film shapes for automatic printers.

Classification and characteristics:

1. The traditional "paper fiber" phase pulp or "paper-based photographic paper" has the highest image quality and durability characteristics by coating emulsion on the traditional pulp fiber. (FB photographic paper for short)

2. The back of the paper is coated with artificial "polyethylene" to prevent chemicals from penetrating the paper-based "resin coated" photographic paper. It can be thoroughly washed in a very short time and is suitable for the treatment of "automatic washing machine". (RC photographic paper for short) A well-treated photo made of FB photographic paper has excellent durability. RC photographic paper is not as good as traditional FB photographic paper in tone.

What's the difference between RC photographic paper and FB photographic paper?

Black and white photographic paper FB is a kind of photographic paper used in black and white photography, which is generally called paper-based photographic paper. FB is the abbreviation of fiber-based. The so-called RC, also called RC directly, is the abbreviation of in-Coated.

Earlier FB was mostly used for photographic paper. In contrast, the newer C photographic paper developed by Kodak Company is popular, but it is questioned more. This problem is manifested in two aspects; On the one hand, it is the performance of preservation. It is considered that the preservation of RC is worse than that of FB. On the other hand, it is doubtful about the image expression ability of RC photographic paper, and it is considered that RC can not fully express the tone texture of the image without FB.

Photographic paper can basically only have two layers of structure. One is a silver salt emulsion layer that can be sensitive to light and show light and shade, and the other is a base material loaded with silver salt images, usually paper base, which we call paper base.

The "black" of the image is expressed by the concentration of silver particles. The denser the silver particles, the darker the color. The "white" of the image is actually the place where there are no silver particles attached at all, that is, the paper-based part. Therefore, the color of the paper base determines the performance of this photo paper in the "white" color; How white the paper is, how much "white" the image can show.

Therefore, white material is usually added between the paper base and the silver salt emulsion layer. The most commonly used substance is barium sulfate, which should be called barium sulfate in Chinese. Then, in order to protect the image, a protective layer will be added on the silver salt layer. So the traditional photographic paper, here refers to FB photographic paper.

Black and white photographic paper RC is called RC because it is added with a layer of PE. PE is the abbreviation of polyethylene, commonly known as plastic resin. Here, the role of barium dioxide and titanium dioxide is equivalent to the role of barium sulfate in FB. As the white part of photographic paper, it is actually commonly known as "whitening agent". In RC, titanium dioxide is used because the adhesion between barium sulfate and PE is not very good.

There is not much difference between FB and RC. Especially the silver salt emulsion layer, which is located on the "whitening agent" and is the most decisive to the image, is basically the same. So what kind of characteristics will RC have because of other structural differences? First of all, in darkroom operation, because RC photographic paper is separated by PE on the upper and lower layers of the paper base, except for the edge of the photographic paper, the medicine is unlikely to invade the paper base. This will make the paper-based part of RC, on the one hand, not worry about a large number of chemicals being soaked, leaving residual chemicals in the paper-based part, and greatly reduce the washing process, and it is easy to dry in the shade afterwards. In addition, it also avoids the phenomenon that the photographic paper swells because it absorbs unnecessary chemicals. You should know that the function of paper base is to provide a stable base for silver salt image. If the base itself is unstable, whether it expands with heat or contracts with cold or other factors, it will be unfavorable to the image above. There is also FB photographic paper, because there is no waterproof PE protection, so it will absorb a lot of chemicals when developing and fixing. In the washing process, it must consume a lot of chemicals and other residual chemicals, and it must spend more time than RC photographic paper to ensure the integrity of the washing process. This process also improves the swelling effect of the basic part of FB paper because it absorbs too much water. Therefore, in this respect, using RC photographic paper can avoid many troubles and risks of darkroom work, unlike FB photographic paper, which needs to be so careful. It is precisely because of these advantages that some beginners like to use RC photographic paper as an entry choice and ask them to develop photos to save time and materials.

In the preservation of black and white photographic paper, if you have some old photos at hand, you may wish to pay attention to whether this side of the photographic paper has cracked in some black and white photos of more than ten or twenty years. The images on many old photographic papers are incomplete. Even if the images are not faded and discolored, there are obvious cracks and folds on the paper base on which the images are loaded. The barium sulfate of FB photographic paper is mixed with gel and coated on photographic paper, which is actually quite fragile and easy to fold. We can also say that FB photographic paper is not resistant to bending because of the great difference in properties between its interfaces, and any bending may cause damage. On the other hand, RC photographic paper, because of its considerable elasticity, is equal to whether it is suitable for long-term storage as a material of two interfaces. We seldom pay attention to the photographic paper itself, and we have hardly heard of the cracking of colored paper, so RC is also used. Some people may say that this is because RC photographic paper did not appear early enough and has not encountered such a thing. I can only say that in my impression, I have read magazine reports that PE materials will not crack even for decades or even hundreds of years.