Page 19 - RD_2015_12

Then another miscalculation was revealed. With black- and-white pictures a speed of sixteen
pictures is the minimum capable of conveying the impression of continuous motion to the brain.
As the pictures are in monochrome, the perfection of the illusion is facilitated. But when it
came to projecting the pictures taken in three different colours, one after the other, this law
was seriously upset. When only sixteen pictures per second are shown, the eye and brain are able
to single out the respective colours. The pictures do not run together to give a natural colour-
effect, but are merely successive flashes of red, green, and violet light. Accordingly, the rate of
projection had to be increased three times at least—forty-eight pictures per second—and the
strain of this speed upon the film was so great that often it succumbed.

Consequently, before colour-cinematography could advance beyond the year 1899—when
the first patent was filed by Greene—the chemist had to be called in once more to accomplish a
miracle and make possible the dreams of inventors. The sensitised emulsion had to be speeded
up to such a degree that it was sensitive even to red light. By this means the film is made
“panchromatic”, as it is called; that is to say, it becomes so sensitive that it will permit an
exposure to be made as rapidly through the red as through the green screen. But “panchroma-
tism” brought its own drawbacks. The film could no longer be handled in the dark-room
illumined with a ruby lamp, for fear of becoming fogged.

It has not been found practicable to impart panchromatism to the film at the time it is
manufactured. I do not mean to say that it cannot be done at that stage, but the demand for
such a film is so small that it is not worthy of present consideration on the part of the
manufacturer. Until colour-cinematography becomes generally practised, those engaged in its
exploitation will be compelled to render their film panchromatic preparatory to exposure.

This means that the film as it arrives from the manufacturer must be submitted to a prelimi-
nary operation to augment its sensitiveness to light. For this purpose it is passed through a
“colour-sensitising” solution. The precise constitution of this sensitising bath is jealously guard-
ed, though the materials employed in the process are well known, and several formulae which
will render a film panchromatic have been published. Any one of three chemicals can be utilised
to render the ordinary film so sensitive to light that the ruby lamp will fog it. These are
pinachrome, pinacyanol. and ethyl-violet. The proportion of these fundamental chemicals varies,
the majority of investigators having evolved a particular formula which they have found to be the
be best suited to their own requirements. The published formulae, however, have proved quite
reliable, and have been productive of some excellent results; and they provide the experimenter
with a basis upon which to carry out his work. Recently a further development has been
recorded. W. F. Greene, the pioneer, has successfully employed a new colour sensitiser, which
is faster than either of the three above-mentioned mediums.

Panchromatising is a tedious operation. The work has to be carried out practically in total
darkness, or at the utmost in the faint glimmer of a blue-black light. Even this slight illumination
has to be used very sparingly, being switched on only for a few seconds at a time. After being

REEL DEALS September 2017 19