Coal-Tar Colours Collodio-Chloride Printing-out Paper
and development. The lens used may be, of course, that usually employed, and it should be racked out to its equivalent focus, and a comparatively small diaphragm used - though this will depend upon the character of the clouds, as heavy, dark thunder-clouds will require a larger aperture than the fleecy clouds of bright weather. For dark masses, as a rule,will be large
enough; whilst for bright sunlit masses on a blue sky as small aswill be found ample. In any case, however, a shutter
exposure will be required; generally fromsec. will be
sufficient. For development of such plates it is advisable to keep down pyro, so as to obtain soft and delicate negatives rather than bold or vigorous contrasts, and the development should not be pushed too far. For sunrise and sunset effects isochromatic plates are a sine qua non; these alone will in any way do but tardy justice to the sometimes beautiful effects to be obtained at these times; but in every case it must not be forgotten that colour must be disregarded, shape and the relative massing of the clouds alone being of any use to the photographers. To print clouds into a negative it is advisable first to take a print on ordinary albumenised paper, and then the outline of the sky should be carefully cut with a sharp pair of fine-pointed scissors, and this mask, as it is termed, should be adjusted on the negative, and the sky printed in on the print after the landscape or sea-scape has been printed. For printing clouds in enlargements and lantern slides the same plan may be adopted, or with the latter the clouds may be printed on another plate, and the same, when developed, fixed, and washed, used as a covering glass. In the finished print clouds should, in almost every case, be subordinate to the landscape, and therefore they should not be so heavily printed - in fact, in some cases the merest suspicion of clouds is quite sufficient to I produce an agreeable effect. For a photographic method of determining the height of clouds see Nephograph.
Coal-Tar Colours. See Aniline Colours.
Coffee Process. In this method Colonel Barrett used in-fusion of coffee as an organifier or preservative of the collodion bath plate.
Collodio-Chloride Printing-out Paper. This was proposed by Wharton Simpson in 1865, and for some considerable time