العناصر الرئيسية في تركيب محلول الإظهار .. كتاب التحميض والطبع والتكبير

The main elements in the composition of the highlighting solution

There are different types of show solutions, each of which contains several chemical compounds that differ in type and weight from one show solution to another. Each compound performs a specific function. The following is a summary of the functions performed by these vehicles:

1- Compounds that carry out the reduction process, sometimes known as Development Agents.
2 - Preservatives prevent and delay the deterioration of the reducing agent. confirm it.
3 - Alkaline compounds to activate the reduction process. Accelerators or Alkali
4- An inhibitor of the activity of the reducing agent. The following is an explanation of these functions and the names of the salts they perform:

First - Display Agents.Developing Agent

Reducing agents are, in fact, chemical reducing agents whose function is to reduce the silver salt, which is usually silver bromide in most modern films, and turn it into black metallic silver.

There are many chemical compounds that reduce, but what is suitable for the purposes of photography is required to differentiate between the areas that were exposed to light and those that were not exposed to it, so it affects the areas that were exposed to a lot of light to a much greater degree than those that did not get a sufficient amount of it. It is also supposed to have no effect on areas that were not exposed to light in the first place, but this last characteristic is not accurately available in many reducing agents, causing what has been termed “fog”.
Reducing agents differ from each other in several ways, which we mention as follows:
A - its ability to remain undamaged:
Most reducing agents tend to oxidize more quickly in highly alkaline solutions than in weak or neutral solutions (such as water). Likewise, the ability of some of them to remain in solutions without deterioration is greater than that of other salts that may deteriorate immediately after dissolving them

B- The degree of their activity as reducing agents:
Sensitive Emulsions. The degree of inherent activity in one salt differs from another, but there are other factors that affect the degree of its activity as reducing agents, and among these factors are the type and quantity of both alkaline and inhibitory compounds in the apparent solution and its concentration. C - Its effect on sensitive emulsions, the heretics argue that some contrast agents may increase contrast (such as hydroquinone), while other agents (calmitol) do not lead to the same effect as before. Among the factors of manifestation is what also leads to an increase in the size of the granules, which is a feature that is often distinguished by the active reduction agents, and the size of the granules decreases when using other low-energy salts, if certain rules are taken into account in the composition of the solutions and the proportions of the other salts they contain.

d - effect of temperature:

The activity of reducing agents generally increases if the buffer solutions are warm.
The rate of manifestation speed varies according to the increase in temperature, and according to what is known as the “temperature coefficient” whose value varies from a reduction factor. etc . This rate is estimated numerically based on the ratio between the two cities showing temperature, the difference between which is 10 C. To explain this, we give the following example: Assuming that the correct exposure time = 7 minutes at a temperature of 24 °C. And that the correct display period that leads to the same previous result = 14 minutes at a temperature of 14 C. Then the heat coefficient = 14, and the heat coefficient usually ranges between 1.8 to 3 for most of the usual reducing agents. Here we also point out that this coefficient also depends on the composition of the solution in general and what other salts are included in it.

E - solubility:

Most of the reducing agents dissolve in water (such as mitol, hydroquinone, and pyro), and a few of them do not dissolve in water alone (such as glycine), but rather dissolve in alkaline aqueous solutions. Therefore, alkalis are dissolved first in water, and then glycine is added to it. One of the reducing agents is that it does not dissolve in sodium sulfite solutions (and this is a feature that distinguishes methol) and therefore the reducing agent must be dissolved first, and there are other reducing agents that may require the addition of an amount of alcohol to the solution
Then sulfite is added to facilitate its dissolution. Below are examples of some reducing agents used in photography and their most important properties.

1 - Metol
2- Hydroquinone
3 - Glycine
4- Pyrogallol and Pyrogallol.
E - Amidol
6 - Para-Phenylene-diamine
7 - Para-Aminophenol-Hydrochloride
8 - Pyrocatechin

1- Methol:
It is a salt that dissolves quickly in water, sometimes causing skin infections for people with sensitive skin, and this effect decreases as the degree of its purity increases – and this salt is considered to be a medium activity reducing agent modifiers, as the degree of its effect on areas that have received sufficient exposure from light is close to the degree of Its effect is in other areas that have not received a great deal of exposure, so this salt does not lead to a high contrast. In many formulations of display solutions published by factories that produce photographic materials, we may find other alternative names for the “mitol” salt, such as “ELON” or ORWO M143 or Monomethyl-P-Aminophenol Sulphate

2- Hydroquinone: Hydroquinone
It dissolves easily in warm water, and its solubility decreases in cold water, and the safety stops the effect of hydroquinone as a denaturing agent at temperatures less than 10 °C, and its activity decreases between 10-15 °C. Hydroquinone is considered an active reduction agent, as it quickly affects areas that have been exposed to light, before it begins to affect areas that have not received a large portion. from him . As a result, the proportion of contrast in the images increases by increasing the proportion of hydroquinone in the presenting solution, and reduces its intensity in the presenting solution when potassium bromide is present.

3- Glycine:
It is a salt that has little solubility in water. It dissolves quickly in alkaline solutions (such as solutions of sodium carbonate or potassium carbonate). It is frequently used in solutions of
Rendering prepared for obtaining fine grains Fine Grain developers. Glycine is an inactive reducing agent, as it takes a long time to complete the reduction process. It usually results in low contrast.

4- Pyrogallol:

It is also sometimes called “Pyro” and it is also called pyrogallic acid. and he . A poisonous salt, its crystals are needle-shaped, transparent, colorless, easily soluble in water, and kept in brown glass containers. It is a slow reducing agent that leads to a low contrast, but it is faulty for the yellowing of the negatives, unless the amount of sulfite is greatly increased, and who! And it is possible to remove the discoloration that affects the fingers as a result of its use by citric acid or acetic acid. Al-Bir and Jalul - in the past - were in common use among photographers, and they knew who had colored their fingers due to Al-Biru.

E - Amidol:
Salt with needle crystals, medium in color between white and gray, kept in tightly closed brown bottles so that the salt does not spoil. It deteriorates quickly in solutions, and then loses its activity as a reducing agent, and the solution turns brown. Amidol differs from other reducing agents in that it does not require an alkaline substance to activate it in the show solution, but is usually content with sodium sulfite salt, which is characterized by a weak alkaline degree. It is often used in highlighting solutions suitable for working at high temperatures, Tropical developers, and it is also used as a reducing agent in the highlighting solutions needed for some types of sensitive papers.

Paraphenylenediamine - Paraphenylenediamine

Light pink crystals that oxidize easily in air. And cause this salt to color the skin of the fingers or anything else that touches it. It is considered a reducing agent Fast if mixed with caustic alkali in the show solution. On the contrary, it is slow. The effect if the alkalinity decreases. And it leads to fine grains if the amount of sodium sulfite is increased in the solution with a little borax. It is usually used with methol and glycine. In the installation of solutions to show colored films, paraphenylene diamine plays a very important role.

7- Para-Minophenol Hydrochloride. Para-Amino-Phenol Hydrochloride:

Paramidophenol Hydrochloride is also known as Paramidophenol Hydrochloride. It is a salt with needle crystals that are between white and light gray in color. It is easy to dissolve in water. It is damaged if it is overheated without being dissolved in water. It should be kept in well-closed brown glass containers. It is a fast reducing agent
Alkaline solutions.

8- Pyrocatechin:

It is sometimes called Phyrocatechol, and it is a colorless reducing agent, chemically similar to hydroquinone, easily soluble in water, and does not cause an increase in the contrast of the image, but rather it has gradient colors. Therefore, it is suitable for showing images of subjects that are characterized by extreme contrast. It does not cause any spots in the image. There is no chemical fog, and it is not affected by the difference in temperature. Therefore, it is a reducing agent suitable for working at very low temperatures (such as Kodak SD 22 solution, and it will be mentioned in a next chapter), but it is greatly affected according to the type of alkaline salts in the presenting solution. It is Slow action with potassium carbonate and very active with caustic soda. It causes the tendency of the solution to turn brown in the image - negative or positive. Pyrokatechin is also distinguished by its ability to perform reduction despite the presence of hypo in the solution, and therefore it is included in the composition of solutions that combine appearance and fixative at the same time (and you will also talk about it in a next chapter).