Patholor

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The following article is taken from a Supplement to

KINEMATOGRAPH WEEKLY, dated 11th December 1924

 

[ I wish we could see the film referred to in the last paragraph,

but at least I have found some stills]

 

About Pathécolor Films

 

The Multi-colour Stencil Process Described

THE promised paper on Pathécolor films was delivered at the Royal Photographic Society

on December 2, before a large and most interested audience, by M. Ruot, who explained

that the process was a system of multi‑colour stencilling. For each colour applied to the

originally black and white film print, a separate stencil had to be cut, the usual number

of stencils for average colour range being six.

Stencil Cutting

In the early Patholor films, each stencil was made by cutting away portions from a printed

film copy by hand, using a sharp knife, and this same way is still used for special purposes,

such as where the area of celluloid to be cut out is large and fairly free from sharp corners. To‑day the bulk of stencil cutting is done by an electromagnetic needle, the mechanism of which was fully described. It is a double pole electromagnet energised by alternating current at a periodicity of about fifty cycles. Close beneath the poles of the magnet and pivoted centrally between them is a bar so set that it can rock backward and forward in a plane parallel with the magnet poles. Near to, but not at, the axis of this rocking armature is fixed a ball‑jointed lever, a second ball joint at the lever's lower end engaging with the shaft of a reciprocating lever, the path of travel of which is at right angles to the armature bar; that is to say, as the armature bar swings under the magnet poles with the action of a balance‑wheel of a watch, the communicated motion through the lever causes the lower plunger to push in and out. This plunger carries the needle point serving as cutter in the stencil cutting.

A usual way of adapting this electromagnetic film cutting tool to its work is to mount it at one end of a pantograph, the other or hand‑guided end coming over a ground glass window wherein is projected an enlarged image of the actual "frameof the film positive which lies under the cutter needle and is to be converted into a stencil.

A Delicate Process

M. Ruot did not fail to make us realise how very delicate some of the lace-like stencils are where the demands of the process call for many and intricate areas of the picture being cut away from a single frame so that each area may take a tint of the same stencil colour.

Yet still, after the stencils are cut, and after any adhering fragments of unremoved celluloid have been got rid of by "touching up" the stencil with a small knife, the gelatine coating has to be got rid of before the stencil can be used in the colouring machine. We were told how difficult is this problem of removing the gelatine without causing the much‑cut-away base to expand or contract so as to throw it out of truth. The simplest solvent for gelatine has been found to be soda hypochlorite (in other words, the clear solution which results when bleaching powder and soda carbonate are mixed together and the precipitate is allowed to settle).

Stencil plates are sometimes so delicate that to get them through without damage, the machinery has to be arranged so that the actuating pawls will engage with the perforations only once in every two pictures.

Applying the Colour

The lecturer concluded his paper by giving a description of the actual method of applying the colour through the celluloid stencil plates on to the positive print which is being turned from black and white to Patholor. Several excellent photographic and diagrammatic slides helped to point the explanation. The colouring machine consists of a rather large drum round the rim of which positive and stencil plate pass, the one held against the other. At the back of the stencil runs a velvet ribbon travelling in the reverse direction to the film on the drum and at three times the speed. This ribbon is kept moistened with the watery aniline dye solution that has been chosen for the stencil colour, the dye being fed to the ribbon from a rotary brush which in its turn dips into a small trough containing the liquid colour.

A great deal has to do with the temperature of the colouring‑room in deciding how generously and how evenly the colour shall be absorbed by the gelatine of the print under treatment. After application of the colour to the appropriate parts of the print, excess is mopped off by a wad of cotton‑wool attached to the colouring machine, after which the filmstrip passes into a drying cabinet. The colouring operation has to be repeated again and again for all tints to be applied, each through its appropriate stencil plate.

Finally, M. Ruot told us that even with the point of practical perfection to which the Pathstencilling system has been brought, it takes a good worker an hour to cut only three feet of stencil strip for a single tinting, and that for certain shading and special effects it is found necessary to‑day, as it used to be twenty years ago, to make use of the paint brush and add the final touches by hand.

At the conclusion of the lecture a film was shown, the first portion of which gave close‑up views of operatives at the Paris Patholor works running stencil‑cutting and colour‑printing machines. The rest of this film was made up of a collection of carefully path-colorchosen examples of Patholor at its best, and very delightful many of the colour‑schemes were. When at the conclusion Olaf Bloch rose topath-color compliment Messrs. Pathon the high quality of these artistically‑coloured pictures, M. Ruot reminded us that if there was indeed art displayed in the colouring, it was the art of many comparatively humble and quite unknown workers in the factory, on whose behalf he accepted the thanks of the meeting.

 

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