"I.B." Transfer Machine (General Description)
from "Colour Cinematography" (1951) by Adrian Cornwell-Clyne
The machinery used today by Technicolor Ltd. consists of two early type dye transfer machines sent to England by Technicolor Corp. to enable the English firm to start output on a reduced scale (20 feet per minute). Owing to the war, no replacement was feasible and as a result of the increasing demand for colour productions this machine has continued to run practically non-stop (week-ends excluded) ever since. It is now said to be running at the increased rate of 120 feet per minute. The machine was built by the I.B. Corporation (U.S.A.) and designed by Mr." Mack" Ames of The Technicolor Motion Picture Corpora- tion (U.S.A.). The machine is four banked, the fourth not being in use (i.e., Yellow, Cyan and Magenta; in that order).
The" blank "is the first stage in the making of a Technicolor printand consists of Kodak 1301 stock (Negative perforated) bearing a silver sound track and picture rebate and in some cases a faint silver picture image known as the" gray" in London, and the" key" in Hollywood.
These blanks are fed on to the machine on the yellow side by means of a continuous feed elevator, a sprocket with a double, normal, and stationary speed, a form of " dog clutch" being fitted between the feed reel and elevator. Each roll of blank is spliced to the preceding one by a normal cement join. The splicing" cue" for synchronizing purposes is printed on the " blank," corresponding to the track negative as edited by the negative cutting department.
The blank then runs from the feed elevator past a mercuroid trip switch into the yellow "pre-wet bath " containing " de-aerated" water . The yellow, cyan and magenta pre-wet baths are long horizontal troughs each running above its appropriate colour" table." The object of the pre-wet is partially to soften the surface of the blank emulsion in order to decrease the chance of transfer due to" air " and to increase the receptivity of the emulsion to the transference of dye.
After. say, two minutes' immersion, the blank emerges from the yellow pre-wet, travels past two blow-offs (one either side of the film to remove surplus water), turns downwards past a mercuroid trip switch, and into the " roll tank " (entering it from the top) which is filled with de-aerated water. This water is kept flowing at a rate of 9 gallons per minute.
It is in this roll tank that the blank is" married" or brought into close contact with the yellow matrix, the blank being uppermost. Both are then seated on the monel" pin belt," by means of pressure exerted by four 6-in. diameter rubber treaded rollers; that is, two above and two below the pin belt. A jet of de-aerated water is directed at the point of first contact between blank and matrix. This is another precaution against the possibility of" transfer for air," a defect brought about by the presence of particles of air trapped between matrix and blank, and so causing transfer of the colour in question. This defect is most liable to occur in areas of great colour contrast (i.e., air particles caught in the shelf" in the" topography " of the matrix surface).
At about the same time as the blank is being fed on to the machine, the appropriate yellow matrix is also being run on to a continuous feed elevator, each roll of matrix being cut to length, for synchronization with the blank, by the matrix make-up department. The matrix is attached to its predecessor by means of a 6-inch length of monel strip (perforated in the same manner as a piece of negative cine film), and by four two-pronged clips.
A driving sprocket with a three-position free wheel, normal, and stationary type of dog clutch, supplies this elevator from the feed reel. Another sprocket carries the matrix into the top of the dye tank, where it runs in vertical paths past two cascades. These cascades are supplied with dye pumped up from a vat below the floor. The dye is passed through three filter bags, one large one in the vat and two smaller ones over the dye tank cascades. Dye corrections are applied by boost- ing every 15 minutes under the direct control of the chemical depart- ment who are advised partly by" hand transfer tests" of a gray scale, and partly by the viewing room.
During its travel through the dye tank the matrix passes over a driving sprocket and a weighted jockey pulley attached to a cord. This cord actuates the speed control arm of a four-bush motor which drivcthis section of the machine. In this way the driving motor speed is governed by the tension of the film.
After leaving the top of the dye tank, the yellow matrix runs down into the" wash back "where it remains for about 90 seconds, travelling in a vertical path past either end of a hot water cascade whose tempera- ture can be easily varied by means of a mixing valve.
The object of the" wash-back "is to wash off the dye superfluous to the amount required to bring about the desired colour ratio. The effectiveness of this washing off is directly related to the temperature of the water used, the duration of the " wash-back" time being constant (i.e., the greater the temperature the greater the wash-off).
It is of interest to note that the main difference between the technique used in the London plant and that used in Hollywood, is that the Americans keep the temperature constant, but control the duration of wash-back." In either case the technique is directly controlled by the viewing room.
From the" wash-back" the matrix passes through a small elevator, the movable element being heavily weighted. This does no more than supply or take up stock in the event of slight sluggishness of the con- trolled driving motors when responding.
From this elevator the matrix passes two blow-offs (one either side of the film), runs downwards past a mercuroid trip switch and enters the roll tank from the top, passing under a roller on to the pin belt where the blank is pressed on to it by the first 6-inch roller and held in register by the pins.
The pin belt is 240 feet long, consisting of monel perforated strip 35 mm. wide, with both large and small teeth soldered in these per- forations. The small teeth are on the " track " side of the blank. The whole length is soldered into a loop. Four wheels of approximately 40~inches diameter enable it to travel from end to end of the machine four times. The two wheels at the dye tank end (termed the " wet end ") are set at a slight angle to each other, to give the desired cross over, and about 6 feet apart. The path from the wheel nearest the wet end passes through the roll tank by means of a water gate either end. The two wheels at the dry box end (" dry end ") run in a vertical plane side by side.
Towards the under side of the upper two paths, which travel from the wet to the dry end, and the upper side of the under two paths of the pin belt (i.e., the side not taken up by the film and teeth) hot water trunking is placed. This trunking is rectangular in section (approx. 6 in. x lj in.). The side of the pin belt bearing the film is protected with wooden covers which are hinged for easy access.
The temperature of this heated surface (known as the " table ") is controlled. The greater the temperature the greater the contrast. There is an increased colour density in the shadows, giving in severe cases " off ratio " defects. It is therefore Technicolor policy to keep these table temperatures constant according to a standard technique by means of mixing valves.
The matrix and blank in close contact, and held in register by the pin belt, emerge from the water gate (nearest the dye end) of the roll tank, and pass under the large seating belt. This seating belt is a loop of copper strip, about 9 inches diameter, similar to a piece of negative perforated cine film, but having smaller perforation on the track side. These perforations are seated over the teeth of the pin belt by the pressure or weight of a large rubber treaded roller, there being also a small roller 3 inches away to assist the" take off" of the loop from the pin belt. The large seating belt is followed by the small seating belt. The latter is similar to the first but only forms a loop 7 inches in diameter. it has only one seating roller and is of less weight.
The object of the seating belts is to ensure the correct seating of the blank and matrix perforations around the pin belt teeth. Incorrect seating of the blank and matrix would cause transfer around the perforations. Results of this are to be seen in the form of half round areas of colour with sharply defined edges against the perforations. The defect is most noticeable on the non-track side. A close contact between blank and matrix is still further ensured by the use of two weighted rollers, the first having a 4 lb. weight attached, and the second having one of 9 lb.
After these pressure rollers a sucker is placed to remove surplus water from around the perforations and pins. This is then followed by a blow- off to remove any surplus water drops from the cell side of the blank. It is on this part of the pin belt between the blow-off and the tables that the" sync. marks" printed on the matrix and blank are checked to ensure against" out of frame" and " out of sync." (out of rack) defects. if such a defect does occur, the number of perforations, frames, or feet, out of sync. are measured and the necessary length of leader attached to the next roll of blank or matrix (whichever is applicable) to be run on the machine.
The pin belt is friction driven by the two dry end wheels, which are chain driven by a constant speed motor. This is the only motor on the colour bank that is not controlled, and is therefore the one that sets the overall speed of the machine, and is termed the main drive motor.
After completing the two circuits on the pin belt, the blank and matrix leave it at a point in line with and about 3+ ft. below the seating belts. The parting is effected by both blank and matrix running over a roller called the" stripping roller "whilst the pin belt continues along its horizontal path.
The blank runs vertically downwards in a flat plane whilst the matrix runs off at an angle of 45 degrees downwards with a twist through 180 degrees. It is this twist that brings about the stripping or parting of the two films. A mercuroid switch is placed on the blank just after the stripping point.
Both matrix and blank run over pulleys (both now being emulsion downwards) and run in horizontal paths towards the dry end, im- mediately below the lower tables. The blank runs horizontally in a dry box from end to end three times before emerging at the dry end to travel to the top of the machine and over a captive diabola (which by means of a cord governs the speed of the matrix dry box drive motor). The drive for the blank dry box is supplied by a friction loaded rubber covered pulley powered by~a chain from the main drive motor.
The blank, after passing a mercuroid switch, travels into the pre-wet bath of the succeeding colour bank (i.e., the cyan).
The matrix after leaving the stripping wheel runs under the blank dry box to a point below the large dry end pin belt driving wheels, where it travels through the floor to the " decro tank containing sodium carbonate (not circulated). The object of this tank is to wash the matrix clear of any remaining dye (a mercuroid switch being placed at the entry into this tank).
After this the matrix passes into a wash tank and then up through the floor into Lhe matrix dry box at the end of the transfer machine. It leaves this to be rolled up on the take-up. After re-winding and inspection by " matrix re-wind dept." it is held in readiness for a further transfer.
The cyan bank is identical to the yellow (the yellow and cyan banks being built side by side in one unit (this formed an original two-colour machine)). The blank bearing the yellow and cyan dye image passes over to the magenta bank. This bank, and a disused one alongside, forms another of the original two-colour machines, and stands parallel to the yellow and cyan banks with a gangway about 6 ft. wide between them. The magenta bank is very similar to the yellow and cyan, but has the following differences. A small tank containing alcohol, with a fixed elevator running in it, is placed between the wash back and roll tank. This is only used when a certain matrix is known to be bad for air and transfer. It is on the magenta that these defects are most pronounced. The softening effect of the alcohol on the dye laden matrix emulsion not only minimises the above defect but also increases dye spread. The weights attached to the rollers after the seating belts are in- creased to 6 and 12 lb. respectively. The table temperature on this bank is maintained 100 F. above that on the other two tables. The last two modifications are introduced in order to reduce the chances of air, and transfer. The blank on leaving the magenta dry box passes over waxing rollers running over the perforation tracks. After this the blank runs past a mercuroid switch, on to the take-up elevator.