This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Autochromes From Autochromes. It is often desirable to make duplicates of the choicest of our Auto-chrome results, first, on account of the intrinsic value of the original, and second, because a copy may be sufficiently satisfactory to loan out to societies and individuals, with the possibility of accidents occurring. For more than one reason, duplicates cannot be equal to the originals, but the following method will give the best possible results: Fix up a camera so that the lens points toward a bright, north, white-clouded sky. Extend the front to the focal-length of the lens, stop the latter down to f. 22 and adjust the light filter. In the plate-holder place the Autochrome picture you wish to duplicate, glass side down, and after cleaning the glass, place the Autochrome plate, glass side down, upon the film of the picture in the holder, backing up with a black velvet-covered card. Put the holder into the camera and expose. The exposure will be about ten times the normal and must be ascertained by experiment. The subsequent operation will be as for direct pictures.
Incorrect Color Rendering. When a general blue tone pervades the whole of an Autochrome picture, the cause must be looked for in more than one direction. In the first place, it may be the result of under-exposure, or what is quite as likely, it may be found that the yellow absorption filter has somewhat faded by exposure to light. On the other hand, there may be a predominence of blue in the light which may not be apparent to the eye; and on cloudless summer days, and at coast towns, this will often be the cause of the excess of blue in the picture. It is advisable to have a deeper yellow screen for use under such conditions; or, as an alternative, a supplementary screen made by dyeing a fixed-out transparency plate in picric acid may be used, together with the normal screen, and the exposure increased accordingly, say two to four times. Blue fog will also develop onto the picture if a trace of white light is allowed to get into the room, especially from under the door. If any other light than that actually passing through the filter reaches the plate during exposure, blue tones will result. A strip of black velvet should be fastened around the filter carrier when fixed in front of the camera, in order to avoid any light creeping between the filter and the lens.
1079. Flat and Foggy Autochromes may be improved by treating in the following manner: Put the Autochrome into a bath of hypo 1/2 ounce, water 6 ounces; soak for one minute, and then add to the hypo solution one ounce of a 3 per cent. solution of potassium ferricyanide. Allow this mixture to act upon the Autochrome picture for one minute, wash for a minute, and examine in a strong light. If not sufficiently cleared, continue the action of the hypo-ferricyanide solution another minute or two, afterward washing for five minutes. The picture must now be re-intensified with F and G solutions, cleared in H solution, and washed. Re-fixing is not necessary.
Reducing Density. Over-intensified or otherwise dense results may be somewhat reduced by immersing for a few minutes in a fresh acid hypo solution. The following method is also successful:
1081. Persulphate Reducer. -
Ammonium Persulphate .....................
1082. Immerse the Autochrome, without previous wetting, in the above solution, and watch the action care-
Study No. 56
Gertrude Kasebier fully. Before reduction has been carried quite as far as is desired, transfer to a 5 per cent. sodium sulphite bath for two minutes. Wash for two minutes, and dry.
Improving Faulty Coloring. A solution of yellow or orange dye will improve the color of blue-toned pictures; and green dye will give a more pleasing tone to pictures in which much pink prevails through over-exposure.
1085. If the light employed is a yellow coal-gas flame, the yellow screen should only be used for half the time of exposure. If incandescent electric bulb, the screen may be used for three parts of the time and, generally speaking, with incandescent gas, with a new mantle, the screen must be used for the whole of the time. Exposure will, of course, depend upon the amount of illumination employed, but will not be less than an hour, at f. 8, under the most favorable circumstances.
Varnishing And Finishing. All Autochromes should be varnished as soon as dry, using either the celluloid or gum varnishes suggested; and they should then be bound up with a cover-glass to avoid injury to the delicate film.
Lantern Projections. Autochromes intended for exhibition in an optical lantern should be kept as thin and clear as possible, consistent with correct color rendering.
1089. If, during exhibition, the lantern objective is capped between each picture, the results will appear on the screen with greater apparent brilliancy. If the slides are allowed to get hot in the lantern, the film of the picture will crack up and the value of the slide be impaired.