To those who have the faculty of translating color into black and white, the sky is rendered more or less gray, in its monochrome equivalent, and never as white as the paper on which the picture is printed. The color and dependent color value of the blue varies with the direction of the light, the atmosphere and the sun's altitude. Facing the sun the blue is almost effaced; opposite, it is strongest and darkest. It is nearly always lighter at the horizon, but in large towns the effect of dust and vapor may reverse this appearance when the sky is seen over the houses. In Spring, when there is an east wind in this country, the blue has a dryness and opacity that is absent at other periods. In the East there is a depth of blueness that is almost black. All these varying conditions of color, luminosity and gradation have to be represented in black and white by various shades of gray.
The task is somewhat easier where clouds are present. Even in Nature wisps of cirrus and the so-called "mackerel sky" greatly increase the idea of depth and distance. These forms of clouds are really simpler to deal with than the bolder cumulus with their strong shadows and perspective.
When we get a gray sky the problem is easier still. It has not the even gradation of the blue sky. The clouds which float across it are usually dark and are not white in the high lights and darker in the shadows than the ground, as is the case with cumulus in a blue sky, and they can be photographed without so much reference to the problems of color. The landscape also is low toned and can be harmonized with less difficulty, most of it being probably lower toned than the sky. There are often instances, however, where the sun shines out brightly after a passing storm, when the landscape, or parts of it, are brilliantly illuminated against a black ground, and are many tones lighter. A good example of this is seen in Francois Millet's April storm effect with rainbow in the Louvre, which has been most effectively reproduced in a photograph. The photograph shows the illuminated portion of the land and woods lighter than the dark sky, as it should be.
It is quite a difficult matter to represent the ethereal blue of the sky by a monochrome process on paper, such as photography, which goes so much beyond mere suggestion. Apart from the technical difficulties of preserving the color value and tones of the landscape objects that meet it, is the task of rendering in some degree the almost unattainable depth and palpitation, as it were, of which we are conscious when looking at it, but which a gray deposit on paper does not at all suggest. We know that a blue sky, as seen opposite the sun, rendered with fairly accurate color relation to the landscape and slight gradation from horizon to zenith, is disappointing in an ordinary platinum print and fails to convey the impression of the original. This is still more marked in the skies of Southern Europe and the East. Have we yet seen Italy, Egypt or India portrayed with the true value of the blue sky in photography ? In those countries opposite the sun it may be said with truth to be darker than anything terrestrial save the shadows. Yet if an attempt be made to sun down the sky to the proper value the result will be unnatural, and the landscape appear as if under snow.
The printing process chosen has much influence. One cannot help feeling that the evenly diffused gradation of photography is at fault. The luminousness of the sky is much better shown in mezzotints and etchings than in photographs, where not only are the gradations arbitrary but the surface is broken up. If the photograph deposit be broken up in some way-partly to be achieved by the use of rough paper, by printing through some material, in the case of a plain sky, or by the use of a process such as gum bicarbonate, where a broken up surface can be left by means of a brush - the sky can be kept more nearly approaching its proper value without appearing too opaque.
The depth of printing of a sky, which we have determined upon as correct, cannot be varied without completely changing the character of the picture. Quite a small difference will suffice to spoil the original intention. It is better to err on the side of being too light than too dark. Clouds too heavily printed will seem too near as well as too solid, and lose their vaporous character. - Eustace Calland in the " Practical Photographer. "
Films, especially those of a Tollable nature, are more difficult to wash than plates. The edges are continually catching in the grooves of the washing tank or else the emulsion surface has a peculiar tendency to rub itself against the sides and bottom of the tank, generally to the detriment of the negative. A satisfactory washing method is as follows: After removing the films from the hypo bath, rinse them quickly in four changes of water, then place them in wash in another tank, changing the water every ten minutes. After the water has been changed eight or nine times, the hypo will be almost entirely eliminated from the films.