The Photographic Film

Development of color negative photographic films

@StefaniaLand

Published in 

Analogue Photography ENG

 · 4 Apr 2021

1.1 Why color

Why was color photography invented if black and white photography already existed?

It was not invented out of pure whim. It was not born to say that one is better than the other. It was created to respond to the expressive need for a new will, for a new reality.
Color photography is the art of making photography as faithful as possible to reality by representing subjects in their shapes, tones, gradations and colors. Colors mean life and reality.
Color is natural because we see in color.
Black and white is an expressive medium that is well suited to abstraction while color photography is much more realistic.
Black and white photos have only two parameters to consider: perspective and contrast. They focus on lines and shapes and the only loss of color helps our mind to imagine the image as abstract and unreal because it is contrary to our perennial vision of the world. In this genre of photography, colors are abstract and translated into black and white in order to obtain contrasts by exploiting the play of light and shadows.
Color photography takes into account three parameters: perspective, contrast and color. In these photographs, color becomes a not negligible element, but rather a fundamental and necessary one. It will be necessary to study chromatic harmonies, saturations, tones and chromatic brightness.
It is therefore clear to think that not all subjects marry with both ways of photographing. The need to research color photography lies in this detail: the two methods are not interchangeable, and if they become so they transmit different meanings to the observer. Some subjects will only look good in color such as a sunset where the magic is represented by its shades of color from red to blue; other subjects will be best highlighted only in black and white such as the portrait of an elderly person where we want to highlight the signs of his life and his history and then we will focus on the wrinkles of the face and not on the complexion or pale skin tone.

1.2 The spectrum of the visual

The human eye does not perceive all the radiations of light and therefore we speak of spectrum of the visible. "White light" is the term used to identify the visible spectrum with wavelengths ranging from 400 nm to 700 nm. These are the same radiation absorbed by the color film.

2 History of the color film structure

It should be noted that the techniques for color reproduction are based on the vision of color perceived by the human eye. Around 1800, Young and Helmholz formulated the theory of color vision based on the analysis of the three-color system and photography was used as a tool to support this theory to see the formation of color in reality.

2.1 The very first experiments for the experimentation of color formation and additive synthesis

Being able to separate the shades of blue from that of green and red from the light reflected by objects has been a difficult challenge for a long time.
The first analysis for color formation is the so-called additive synthesis or RGB.
First studied by Clerk Maxwell, it combines the primary colors of light: red , green and blue . By mixing these colors in different proportions, the whole spectral range is obtained and the sum in equal quantities of the three different radiations gives the white color.

Here the base light is projected through red , blue and green filters.
By adding the primary colors together we obtain the secondary colors (cyan, magenta and yellow).
But how does it work? The filter absorbs all color radiations from white light except those of the filter color itself, the only ones that will be transmitted.
The experiment consisted of exposing three plates of film exposed through the technique of the sum of the primary filters, through three separate filters and lenses, a sophisticated prism and a mirror for the camera to divide the light beam from a single lens to a triple package. All of this remained just a theory with no practical experimentation.

However, the idea remains the basis of today's color vision, and in 1861, James Clerk Maxwell presented his first demonstration of color photography. He recorded the images in three negative black and white films each created with a different color filter. The negative will be blackened only where it has been hit by light and transparent where no ray of light has reached. These were then rendered in positive and projected with the colored filter on a neutral support. This will be the method for discovering color photography despite producing positives (slides).

2.2 Subtractive synthesis (CMYK_ quadricomia)

In order to obtain negative films and positive prints, it will be necessary to use the reverse process called for the note subtractive synthesis or CMYK.
This method proceeds in the opposite way to additive synthesis, so the colors in the subtractive synthesis are the result of reflected light and the primary colors to be used are actually the secondary colors of the additive synthesis.
To obtain a negative on the support and therefore a positive on the paper of the final print it is therefore necessary to play with opposites. The double band complementaries of red, blue and green are used.
In short, to capture the red we do not make the red areas black, but we use a dye that absorbs the red light and allows the green and blue radiation to pass through. Let's talk about cyan or cyan.
For the green, a magenta-colored gelatin is used which absorbs the red.
For the blue filter, a yellow gelatin is used which absorbs blue. By using these three jellies instead of the silver negatives, the filters and the three projectors can be eliminated.

Color combination scheme:

• magenta filter = blocks only the green ray and passes blue and red yellow filter = blocks the blue light and passes red and green
• cyan filter = blocks red and passes only green light and blue light

Combinations of two colors:

• magenta filter (blocks green ) + cyan filter (blocks red ) = return blue
• cyan filter (blocks red ) + yellow filter (blocks blue ) = passes only green
• magenta filter (blocks green ) + yellow filter (blocks blue ) = only red passes

Where the light passes through all three filters, we have no passage of light and therefore we get black

2.2.1 The multilayer film

A multilayer film is made up of all three emulsions (blue, green, red) in the same support trying to minimize and cancel the disadvantages of the previous method. Kodachrome film was the first to be introduced to the market with this capability and was released in 1935. The three emulsions are separated by a layer of gelatin, and coexist safely on the substrate with a layer of halo filter.
This is the principle on which modern color photography is based.

2.2.2. Wholemeal tripacks

Many color films, regardless of positive or negative, are integral tripack films. "Integral" is a term used whenever there is more than one emulsion covering a single base.
An integral tripack consists of a single film base with three light sensitive emulsion layers and coat one side of the substrate. Each layer is responsible for responding to a particular region of the light spectrum.
The three emulsions are not separable and must be worked and developed together.
Structure of an integral Tripack.
An integral tripack emulsion consists of: (1) a suitable base; (2) an antihalo coating; (3) three individual light-sensitive layers; and (4) thin gelatin layer used to separate the sensitive portion of the film from other functions such as filters. The total thickness of the tripack emulsion is approximately 0.0254 mm (25.4 x 10-3 mm). Each individual layer is 5 to 10 times thinner.

3 Section of a generic modern color film

1. An anti-abrasion overcoating protects the film from minimal abrasions.
2. The blue sensitive emulsion layer is where blue is recorded and is the most transparent of all.
3. The yellow filter layer is a layer of silver nanoparticles integrated into the film. The purpose of this filter is to completely capture the blue radiation in order to record only the green in the next layer.
4. The orthochromatic layer is the layer in which green radiation is absorbed.
5. The clear gelatin is a layer to prevent the two emulsions from contaminating each other. It is a security measure
6. The panchromatic emulsion is the layer where the red radiation is recorded. This emulsion guarantees a low sensitivity to green color.
7. The Antihalation layer is the antihalation layer, usually black in order to completely absorb all the radiations of the color and thus avoid any reflected light which, returning back to the already exposed layers, would damage the final image.
8. Film Base is the support for spreading the sensitive emulsion

3.1 Color characteristics

Color can be identified by three properties: hue, brightness and saturation.

1. The word tint means the general color assigned to the subject in question. By saying that an object is red or blue, we identify the color without going to distinguish between the various shades (physically represented by all the radiations contained in the spectrum portion).
2. Brightness is another parameter used to describe a color: dark blue, blue clear. The adjectives light and dark try to indicate the brightness of the color although it is a subjective value. They measure the absorption and reflection capacity of the object.
3. Saturation describes how pure a color is and consequently how bright it is. A non-pure color is usually monotonous and loses attention. Saturation is established by comparing the color with a neutral gray of the same brightness.

3.2 General characteristics of a photographic film

- Sensitivity (ISO - DIN): it is the blackness capacity of the film with the same light ISO

values: 12 - 25 - 50 - 100 - 200 - 400 - 800 - 1600

• low sensitivity (12 iso - 100 iso)
• medium sensitivity (200 iso - 400 iso)
• high sensitivity (800 iso - 1600 iso)

- spectral sensitivity: panchromatic film (sensitivity to all visible wavelengths of light, including red)

- positive or negative

- dimensions:

• small size 24x36
• medium format 4,5x6, 6x6, 6,5x9
• large format 6,5x9 and up

- exposure latitude: it is the ability of an emulsion to tolerate errors in exposure (overexposure, underexposure). It is measured in f / stop (in stop or EV).

• in color negative films: 3 1/2 stops (tolerance of -1e1 / 2 stops; +2 stops)
• in color positive films: 1 stop (tolerance of -1⁄2 stops; +1/2 stops)

- sharpness: the higher the lower the sensitivity because the crystals fit together better -> greater sharpness

4.1 Development of the negative color film

Attention, keep the working temperature according to that suggested by the manufacturer, it will be necessary in order to cancel the color questions and have a balance between the colors themselves.

Phase 0
Pre-wash: its function is to heat the tank and the spirals to the right temperature in order to have greater control of the temperature during the development phase and to avoid significant and not negligible thermal drops.

Phase 1
Bathroom 1_ Color development = chromedogenic development: the one who reveals the three colors of the image imprinted in the film emulsion. Rotation is essential to replace the molecules oxidized by the reaction and therefore allows you to always put in contact new good molecules on the emulsion.

• Phase 1a Stop with 3% acetic acid (any stop of black and white). Instantly blocks the color development function and avoids "polluting" the Bleax.
• Phase 2a Quick rinse to remove all traces of acetic acid in water for 30 seconds. The temperature is the same as that used for development.

Phase 2
Bathroom 2_Bleach (Bleach) + Fixing (Fix) (BX) = this bathroom can be combined in a single solution as happens with the Tetenal house or it can be separated into two distinct solutions. The bleach or bleach is the one that gives brilliance to the colors and makes them vivid. The fixing instead fixes the image over time and allows you not to lose what has been developed.

Phase 3
Washing with water = 30 ”rotation, it is emptied and filled following the same procedure

Phase 4
Stabilizer = hardens the emulsion, protects it from any damage and allows the color balance to be maintained over time. In addition, it is also the "anti-drip" chemical element that helps eliminate a deposit of limescale contained on the film during drying. It often contains formaldehyde, a substance declared carcinogen by the European scientific community.

Pay attention to the sensitivity of the films. The approximate number of developable rolls recommended by the manufacturer, with a certain amount of solution, refers to a certain ISO sensitivity. A roll with higher sensitivity means a greater effort on the part of the acid to obtain the same result in the development seen and considering that we do not change the acid concentration as happens for example in black and white. For this reason, the manufacturer recommends creating fresh acids more often than the declared nominal sensitivity (generally 200 ISO) in order to always obtain optimal results.
Tetenal example:

• 16 ISO films max 200
• 12 ISO 400 or higher films

4.2 The chemical process

The chromodogenic development acts directly on the impressed silver present in the various layers of the emulsion by oxidizing and, as a result, it acts with the color couplers of the film. It must be remembered that the color film is made up of several layers, some of which are selectively sensitive to a certain color. To obtain the finished negative image, it is therefore necessary to transform the impressed halide into metallic silver and at the same time start the coupler procedure which, combined on the various layers, leads to the definition of the correct chromatic balance of the image. Once the color has formed, the subsequent bleaching bath causes the removal of the metallic silver from the support, leaving only the colored and developed image. The last step, fixing, is similar to what happens in black and white development: it allows the removal of all the unimpressed and undeveloped silver still present on the emulsion.
The last steps consist of the final washing which allows to eliminate the fixing residues from the film, and of the stabilization, in which the stabilization of the various colored pigments is carried out by means of chemical agents in order to preserve the balance of the colors over the time.