PHOTOGRAPHY.

Auckland Star, Volume XLII, Issue 287, 2 December 1911, Page 15

PHOTOGRAPHY.

■ '-"♦ — ■ ■ THE FUTURE OF COLOCR-PHOTO- . "^APHY. There is no more fascinating problem in the whole domain ol sc.euce iduui tuat of photography in colours, and there is none in which the ditiiculties appear so insuperable. The solutions that have been proposed up to the present are placed in two groups, One contains all "three-colour" processes, direct Or indirect. The other comprises the so-called Uppmann interference method. " ine former cut the Gordian knot instead of untying it, and -the latter has never progressed beyond a laboratory experiment aim it is doubtful if it ever can do so The Lippmann process has been earned out successfully by a few experimenters, but it requires a good deal of manipulative ability. A sensitive emulsion so fine in grain as to be practically transparent is made and coated on to glass. The plates are exposed in a special holder which allows metallic mercury to be in contact with the film, forming a mirror, on which the image impinges, the glass side of the plate being turned towards the lens. The image is developed and fixed, and then, when it is viewed at a particular angle, the colours make their appearance. Beautiful as is the process, and full of interest as a physical experiment, there can be little doubt that it will never be anything more. "The theory of the process is that a series of maxima and minima of light action is formed on the film by the reflection of the light rays upon themselves by the mirror of mercury; and the film when developed has recorded these as » series of layers of deposit, representing the maxima sepaTated by transparent layersthe minima. These layers have been seen, and have actually been photographed." The three-colour process in its many varieties hardly attempts to give what the man in the street would call colourphotography at all. He uses the expression, so far as he has any definite idea of it whatever, as implying a process of automatic and mechanical a3 he believes ordinary photography to be; giving a faithful rendering in colour, just as the photography he knows gives it in black and white. It must not be a transparency in glass, which he persists in calling a negative, but must be on paper or at least on some opaque support, so that it can be framed or hung up like a water colour or an oil painting. A photographer would say that he does not use the term colour-photogra-phy in anything like so narrow and restricted a sense, but to the great majority this description fairly describes the meaning they ascribe to the phrase. In this sense, how far are we to-day from the achievement? The discovery of some substance which, when exposed to the action of light, would give a product of the same colour as the light which was acting upon it would be a solution on the lines r>f the ordinary photographic process. II this substance could be coated upon glass, and if the coloured products were transparent, so as to transmit as well as to reflect rays of their own colour and were permanent, and if the images so obtained could be ' fixed ' in the photographic sense, by the removal of the unaltered sensitive substance the task Would be accomplished. But what a series of 'ifs'! At present there is no substance which in any circumstances can be given the whole range of known colours, much less assume them under the stimulus of light. Nor is there any sensitive product which can be relied upon to give even one colour with approximate accuracy when exposed to light of that colour. J During the last few years several ex- | perimenters, and particularly Doctor Smith of Zurich, have been working on I a blea.cbing-out colour process. Although in essence a three-colour method, such a process would be a great deal nearer the popular idea than any of the other three-colour methods. Doctor Smith has succeeded in making a paper, which, orig anally dark gray in colour, gradually bleaches to a hue which is approximately that of the light which causes the bleaching. The paper is anything but sensitive, a print from a coloured transpar- ! ency on glass requiring many times as , long as would be needed to give a print on photographic paper from an equallytransparent negative, and so far no method of fixing the prints has been fully successful. The method, however, crude, at present is at least promising, pointing as it does directly towards a result which would be accepted by the public as colour-photography. It should be explained in conclusion that the term three-colour process is indefinitely employed for any photomechanical process of reproducing in colour applicable to either stone or metal. !In this sense, to quote one authority, j" the general process consists in first j making three photograph negatives of the same subject through three different | colour screens representing the three i primary colours, red, yellow and blue." il-Tom 'these three negatives printing j blocks are made. The underlying principles are those of colour-photography, in the vague sense of the term, i