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.
Printing. The only difficulty in printing bichromate paper is in the lack of the appearance of an image. With certain colors-greens and reds, for instance-there is a slight outline shown, but with the heavier tones-blacks and browns-there is no image visible. However, as the latitude of the paper, as stated in a previous paragraph, is very great this difficulty is only apparent, and not real. With the formula first given, that is, the plain bichromate of potassium sensitizer, the sensitiveness of the paper is not so great as when bichromate of ammonium is used. Gum bichromate paper is not as sensitive as carbon tissue, therefore requires longer printing. Generally speaking, the length of exposure of a sheet of gum bichromate paper under an ordinary negative will vary from fifteen minutes to half an hour. In order to print accurately it is advisable to work with an actinometer. A simple devise is fully described in paragraph No. 145.
444. With a good standard negative, make some test exposures with strips of gum-bichromate paper, exposing the slip of paper in the actinometer at the same time you are exposing the test strips, and when the correct tint on the meter has been discovered, that negative can be marked with the time, and from that negative all other negatives can be gauged. As with all daylight printing processes, it is advisable to print a thin negative in diffused light and a strong negative in sunlight.
Developing The Print. After printing, the paper can be developed immediately. Development can take place in daylight. For developing two large trays should be employed, considerably larger than the sheet of paper being used. Fill the first tray three-quarters full of cold water, and in this tray immerse your prints with a sliding motion, face up. The surface of the print should not be touched with the fingers, for if the paper is under-exposed the color will come away almost immediately, and especially wherever it is touched.
446. If properly exposed it will take several minutes before the color begins to come away from the paper. First of all, the water will discolor yellow from the bichromate solution, and therefore, it is a good plan, after the print has been in this first water for several minutes, to remove it to the second dish, which is also three-quarters full of clean, cold water. When the print is perfectly limp, and provided it is not under-exposed, it can be raised from the water; then replaced in the water, face down, and left to develop itself. Any air-bells adhering to the paper must be broken up, of course, on either surface of the paper.
447. A correctly exposed sheet of paper will fully develop by itself in from fifteen minutes to three-quarters of an hour, and if the coating has been done carefully and smoothly,and the pigment used is of a very fine nature,the resulting image will be almost as fine in detail as a silver print. When all the detail is clear, the shadows transparent, and the high-lights clean, the print can be removed from the water and laid flat on the back of a dish or stiff card-board until
152a semi-dry, when it can be hung up to dry by itself. If hung up in its wet state the colors are liable to streak a little. If the worker chooses to alter the nature of the image at all-to work in clouds, change the background, eliminate telegraph poles, or do any other work of that nature on his print-it can be done either while the print is floating face up in the water, or the print itself, when thoroughly wet, can be placed on a board or on the back of a developing tray, and inclined in a tray of water at an angle. Then with a soft camel's hair brush, or with a jet of water from a tube attached to a faucet, all kinds of manipulating work can be effected.
448. The most practical plan is to place the print on a sufficiently large board, which is inclined in a wash-bowl or sink, and apply the water to the print from the end of a rubber hose. By pinching the mouth of the hose the force of the jet of water can be increased or reduced, and by bringing the mouth of the hose near to the print, or removing it, all kinds of spray effects can be produced on the print and clouds can be readily worked in, or other work done, by those who are skilful in drawing, etc.
449. If a print has been over-exposed, this will soon show by the color refusing to come away from the paper in the wash water. In that case the temperature of the water should be raised gradually higher and higher. Or, water can be poured on the print when the latter is on an inclined board, from a height. The force of the water will tear away the color particles, leaving only those parts which have been more thoroughly affected by light. All kinds of implements are used by various workers for working on the print, such as tooth-picks, stiff bristle brushes, etc., depending entirely upon the result desired.
450. Manipulative work on a gum-bichromate print is entirely individual in character. No set rules can be laid down, and the worker as he gains increased experience will evolve methods and ideas for himself. Many workers prefer to over-expose their paper, as this will give them greater latitude for individual work on the print, and not infrequently an expert gum-bichromate printer will work for hours on his damp print to obtain the results he wishes.