Processing
Processing is the term given to the chemical procedure of development of the latent image to produce a visible image and its subsequent stabilisation.
Importance of Processing in the Conservation
and Preservation Domain
Sometimes processing is not considered as a phase of major importance in the domain of Film Preservation and Restoration, because it is often carried out as a "standard" process in large laboratories where restored duplicates are processed together with current productions' negatives and positives. Nevertheless, processing must be considered as an integral part of the Restoration process. Only by carrying out correct processing, we can aim at consistent and high quality results in Restoration.
A modern processing machine
There are a full range of problems and defects that an incorrect processing can introduce in our precious duplicates and prints. However, processing plays also a positive role in the duplication process. Duplicating archival materials is a complicated matter, which often requires working with non-standard materials (i.e. materials whose standards are nowadays forgotten, or film materials which are obsolete) and this might require non-standard solutions. Therefore - particularly in the case of B&W - we might need to overdevelop or underdevelop our duplicates in order to obtain the required contrast and density. In other cases, the process of duplication is so delicate that the smallest lack of continuity or consistency can result in a disaster (e.g. when processing B&W separations from colour negatives).
Therefore, processing becomes a phase of the greatest importance, and the staff doing this part of the work must be particularly knowledgeable and careful. In fact, they have to deal with two apparently contradictory needs. On the one hand, they must ensure the maximum level of consistency of the process, so that grading, printing and duplication can rely on consistent results, both in general and during each restoration. When a Grader decides that he is aiming to a certain contrast and density, and the person in charge of printing operates accordingly, they must be sure that - today, tomorrow or in two months - the results will correspond to their expectations.
On the other hand, processing must also ensure the same level of consistency and quality while providing a great level of flexibility when it is requested to modify its standards and parameters in order to meet the needs of non-standard duplication processes and routes.
To summarize, to perform high quality processing means to ensure consistency within a frame of flexibility, and to provide materials which are always clean and free from defects induced by processing. These are not easy tasks.
The first photographic materials were emulsions coated onto glass plates or paper and for still photographs were processed by being placed in the chemical solutions in a dish or small tank. The dish was rocked back and forward to agitate the liquid and produce an even chemical reaction.
Later (about 1885) celluloid film sheets were also used as a base and the film was processed in the same way or hung on clips in a deep tank of solution.
A tank used to immerse racks into developer
When the first process (the development) had finished, the material, on its clip, was lifted out, drained of surface liquid, placed in a water rinse and after this in the fix solution tank. By 1895 the approximate timing of the procedure was: development, 10 min., rinse 30 seconds, fix 15 min. and finally wash in water about 15 minutes
Some variation occurred, an acid stop bath replaced the rinse, and sometimes a hardener solution was inserted before the last wash. These early emulsions were very soft and could occasionally detach from the base and float away in the water.
It is difficult to know how long the earliest films were at the outset of cinematography as no films remain in archives from this period longer than a few metres. The first celluloid films were made in 200 ft length batches and in 1900, films were being processed in batches of about 60 metres (200 ft).
Checking if the developing time is sufficient before removing the rack
from solution.
Early cine film continued to be processed in about 200 ft lengths until the late 1920's although a few large companies patented and presumably used, simple continuous processing machinery from about 1920. Most film was batch processed. The 200 ft was wound round onto one of several different designs of rack before the entire rack was lowered into the processing solution.
"Pin-frames"
were flat wooden crosses with pins or nails to allow the film to be wound on in
a spiral. The solutions were in flat dishes.
A "Pin-frame"
Another method was to
wind the film onto huge drums 1-2 m in diameter and 2-3 m long, in a helix. The
drums were dipped into the solutions and rotated to keep the film wet and
agitated. These drums were also used to dry film and sometimes film processed
on racks was rewound onto the drum while wet for drying!
A "Drum"
Another system consisted of two 50 mm diameter wooden bars about 2-3 metres apart, the film wound helically about 15 times, and the ends of the film secured to the frame. These were called frames in England and "racks" in the USA The racks were weighted and lowered into deep tanks, often made of porcelain up to 3 m deep. After the development was over the rack was lifted, held to drain and moved on to the next tank for the next stage. In some literature there seems to be a distinction made between racks which were as described above and frames described as a rotating bundle of rods around which the film was wound.
A "rack"
|
A laboratory in the silent era. Loading racks in the darkroom and unloading racks and drums after drying. |
About 1905 it seems someone (in the USA) thought of keeping a rack in each tank and pulling the film over the roller like bars in a helical manner and onto the next tank rack as there were a number of patents issued. Some ideas seem to be unlikely to be successful but by 1910 at least some mechanised processing was being done in USA, England, France and Germany, but very little is known about the exact details in actual laboratories.
From 1920, onwards there were a very large number of patents issued but whether this meant that continuous processing was common, it is difficult to be certain. The main improvement next came between 1938 and 1965, when it became possible to process the complex multistage colour processes at high speeds, that is faster than about 20 ft per minute.
An early processing machine
From the 1920 3-stage black and white process at 20 ft/min [400 m/hr -one quarter of the speed of a camera] to today's colour processors at 11,000 m/hr or 600 ft/min with up to 25 or more stages. This required the invention of modern drive systems that can handle film gently at constant adjustable tensions as the film extends when wet and shrinks back as it dries.
The technician in charge of processing should be familiar with the process specification of all machines, including the time, composition and purpose of each bath. In the case of colour processes, obtain this information from the manufacturer's specification sheets and processing manual.
There are four types of motion picture process
Whether colour or black and white they all fall into one of these categories. The positive and negative processes are similar, differing only in the activity of the developer. A positive developer is more active producing higher contrast, the negative developer less active and lower in contrast. We can consider contrast as the number of tones or greys between black and white. A film with very high contrast would have only black and white tones. A low contrast film has a large number of greys between black and white.
Film at its most basic consists of a transparent support, the base, coated with a light sensitive emulsion consisting of silver halides.
Washing and drying are as important and as critical with colour film as with black and white.
Types and
Technical Characteristics of Processing Machines
Operating a
processing machine