عيوب الصور السالبة وكيفية إصلاحها .. كتاب التحميض والطبع والتكبير

Chapter VI

Negative defects and how to fix them

First: INTENSIFICATION INTENSIFICATION

It is a process whose purpose is to increase the blackness of the image if it is deficient in density, which is the defect that usually results from underexposure, underdevelopment, or using a weak or exhausted appearance solution, as may result from all of these errors together. In addition to the disadvantage of lack of intensity (caused by previous errors), the degree of contrast is also often less than the desired limit, or the details of the low-light areas or shadows are less clear.

Increasing the density of negatives:

We can summarize the functions performed by thickening solutions in the following two items:
(a) Adding a thin metallic layer over the existing Silver Image.

(b) Or increasing the ability of the image to resist the passage of the effective rays that affect sensitive paper or film: when printing or enlarging to obtain a positive image, which results in the final result with the process of increasing the density, although it may not result from this process. An actual increase in the density of the negative image.

In both of the previous cases, the extent of the density increase (which we expect) is directly proportional to the degree of blackness in the parts of the negative image that we would like to improve, meaning that if there are intensely black areas in the image originally and other areas adjacent to it that are less black, then the density increases a lot in the dense areas. Originally, while the density does not increase in the less black areas, the increase is slightly, but the areas that were completely transparent in the negative image do not increase their density at all. Thus, the process of increasing the density results in an increase in the degree of contrast as well. We conclude from the foregoing that the process of increasing the density is not feasible if the negative image has a very low density, that is, if it is very light and highly transparent. Therefore, we do not expect, for example, that the image will improve much if its exposure or display is very incomplete, or if it suffers from both defects.

As a result of the process of increasing the density, the size of the particles also increases greatly, with the exception of one case, which is the increase in the density with silver, which we will explain later.

Ways to increase the intensity of negative images:

There are several ways to increase the density of negative images, summarized as follows:

(a) Density increase with Baker's salt and potassium matt.


(b) Density increase with mercuric chloride salt.


(h) Density increase with silver nitrate salt.

(E) Density increase with uranium nitrate

(e) Increasing the density to its maximum (by hypo and hydroquinone)

(f) Intensity-intensity staining of the image

Important notes regarding the process of increasing or decreasing the density:

It is likely that the image will be damaged or irregular color or spots will appear on the negatives that will be subject to repair operations following the image fixation process. To get rid of the previous damages:

(1) The image must be fixed and washed completely before starting repair operations.

(2) To increase its hardness (especially if the weather is hot) by treating in one of the hardening solutions prepared for this purpose. Such as Kodak Prehardener S formalin hardening solution (1) or Gevaert 354 solution (p. 194)

(3) The image being repaired must move continuously during its treatment in the repair solutions.

(4) The image should be washed with water well after treating it in solutions, and the water should be removed from it, then dried.

(e) It is better to use special handles for films (Fig. 18 b p. 38, 19 p. 39) instead of holding them by hand, as the salts used in this process are often toxic, and some acids that are harmful to the skin are frequently used. On the other hand, it may result in Holding the negative by hand means that traces of fingerprints are printed on it, and these traces are clearly colored when the film is treated in different solutions.

First: Increasing the density using potassium bichromate salt:

This process is carried out in two steps, the first is a whitening process, and the second is a resurfacing process.

(1) The process of bleaching. This designation aims to remove the black color (caused by silver) from the negative. To achieve this, the negative is treated in a solution known as the bleaching bath, consisting of a solution of potassium bichromate with dilute hydrochloric acid.

(2) The redevelopment process. Once the whitening process is over, the film is washed with water well until the yellow color is removed from it, then it is re-appeared in a strong bleaching solution (mitol-hydroquinone). It is not permissible to use bleaching solutions that lead to fine particles in this process. The following are examples of the composition of bleaching solutions.