المعاملات الكيميائية اللازمة لأوراق الطبع في ضوء النهار التي تستلزم تلوينها .

Chemical treatments required for daylight printing papers that require colouring:

The operations required to show the image are summarized as follows:
Washing - Toning - Washing - Fixing - Washing There are special solutions that combine the processes of coloring and fixation. We will talk about each of the previous steps below.

1) The first washing process:

The first washing process dissolves all the water-soluble silver salts, which are the salts that remained after the exposure process and which did not turn into metallic silver. The first process takes about 30 minutes in running water. The tap water turns milky white in a Milly color due to its mixing with dissolved silver salts, so it can be verified that the necessary washing process has been completed completely when the water color remains clear and transparent.

b) Daylight leaf coloring process:

The coloring solution consists of two equal solutions of:

gold chloride 1%
Ammonium Thiocyanate 10%

Then the mixture is diluted with water in the proportion of one part of the mixture to fifty parts of water. Every 100 cm of the diluted solution is sufficient to color 700 cm of the pictures. The mixture should not be used before two hours have passed since the start of its installation. The time required to treat the picture in the previous solution is estimated according to the degree of coloring required and the extent of the solution being exhausted.

After the color of the picture reaches the required level, it is washed with water well for ten minutes in running water, then its fixation begins.

C) The process of installing daylight sheets:

These papers are fixed in a 20% hypo concentration solution, and it is wrong to install them in acidic fixation solutions. It is taken into account to move the images throughout the fixation process, which takes a period of not more than ten minutes, but if it exceeds that, it is possible that the image density will decrease, and therefore the fixation period will be deliberately increased if the image density increases by mistake as a result of overexposing it. This is enough for every 100 cm of the solution to fix an area of ​​paper of 1500 cm.

As we mentioned earlier, it is possible to combine the two processes of coloring and fixing in one solution, as an example of that the following solution:

d) Washing and drying:

After the fixation is complete, the image is washed in running water for a period of not less than an hour. If the running water was not available, the water basin should be changed every five minutes, i.e. at a rate of 12 times per hour. Then the images are dried in the usual ways.

Reflective photoprinting:

This method is suitable for photographing writing or line drawing on paper, and we summarize the following as follows: the “mechanism” of this process: the rays first pass through the sensitive paper, then they are met by the blue or the written document to be photographed, which consists of white parts (the surface of the paper) and black parts If it is encountered by black or colored ink, it absorbs it (Fig. 50), but if it meets white paper, it reflects it on the sensitive paper, and affects it with a light effect that makes it black when performing the display process.

Here is a summary of the difference between the two methods of printing mentioned above:

(A) In printing by the reflective method of non-transparent written originals, such as documents - documents - drawings, etc., the rays first pass through the sensitive paper, and the light effect takes place on the sensitive paper by means of rays reflected from the white parts of the document or the original document.

(b) In printing positive images from a transparent negative, the rays first pass through the negative. The optical effect is done in sensitive paper by interspersed rays.
There are various devices that serve this purpose (Fig. 52), and they usually contain three colors of light, which we describe as follows:

1- The red light: the stripper is used to arrange the sensitive paper in front of the document to be photographed.

2- Yellow light: It is used as a light filter to help prevent the appearance of possible writing on the back page of the document to be photographed. - White light: It is the one that affects the sensitive layer for printing waveforms.