MONOCHROME, RENDERING COLOURS IN The ordinary photograph is limited in the sense that the various colours of the original are all recorded by different shades of grey or monochrome. Should a yellow daffodil be placed in front of a violet screen, the yellow of the flower and the violet of the screen both being equally bright, the eye would at once differentiate them owing to the colour contrast. A fully iso- or ortho-chromatic plate would record them in the negative as of exactly equal tone. An ordinary plate would render the violet screen almost white, the yellow daffodil almost black. Both results would be wrong.
The ordinary photograph is all of one colour, hence the rendering is in monochrome, and we are dependent on monochrome contrasts to repre sent both light and shade, and colour contrasts. How a correct rendering in monochrome of a coloured subject can be effected will be seen by a reference to a plate accompanying this work : " Various Renderings of Daffodils in a Blue Vase." The left-hand top picture shows an absolutely incorrect rendering, as is inevitable when using an ordinary plate which is practically insensitive to yellow, hence the flowers appear nearly black. The blue of the vase is intensely actinic, and in consequence appears white. In the top right-hand picture is shown the same subject recorded orthochromatically, the vase appearing dark and the flowers light grey. By slightly overdoing the colour correction a picture is obtained (bottom right-hand figure) which gives an excellent contrast between flowers and vase. It will thus be seen that by
intentional wrong rendering in monochrome it is possible to suggest to the eye the colour contrasts that it would see in the original subject.
In the spectrum, the brightest colour, to the eye, is the greenish-yellow ; apple green and orange are the next brightest ; blue-green and orange-red less bright ; and violet and ruby least bright. When a perfectly correct colour rendering is required, the plate and the screen must be so combined that on photographing the spectrum the various pure colours would be recorded in monochrome in the order given, greenish-yellow (lightest), green and orange, blue and red, violet and ruby.
The monochrome gradation is again altered according to the colour of the print. An ordinary subject, such as a cottage or house, appears very " flat " in a yellow carbon print, and much brighter or more contrasty if printed in pink, green or blue. The tone values in each print, relatively to each other, would be the same, but the apparent contrasts to the eye would vary greatly. Where subtle contrasts require emphasis, a warm colour such as sepia should not be employed for the print, but either a bright grey, such as would be given by d gaslight print, or a blue tone.