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The Barnet Book of Photography A Collection of Practical Articles

When recrystallized bichromate is not procurable


The

sensitizing _may_ be done in ordinary daylight. The drying _must_ take place in a room from which actinic light is excluded, and in a current of warm dry air, free from impurities, such as the products of combustion from burning gas, or an escape of sewer gas, etc., and at a temperature not higher than 120 deg. F. The drying should be done as quickly as possible, otherwise the tissue's keeping property will be greatly reduced, and in all probability a thin film formed on the surface, of insoluble gelatine, known to printers as "decomposed tint," degrading the high-lights, and, except in the case of very "hard" negatives, spoiling the work.

It will be evident to anyone that the fancy forms of sensitizing have been carefully avoided--floating on the back, floating on the face, etc., etc. All the results desired can be obtained by immersion. If a hard negative has to be dealt with, a stronger solution, or longer soaking in the bichromate solution, is all that is needed; for weak negatives _vice versa_.

_Note._--In the dry frosty air of winter, sensitized tissue will dry without heat, and continue soluble for a considerable length of time, often as long as a month, or even longer.

In hot weather it is recommended that the solution of recrystallized bichromate be made immediately before using, as in dissolving the crystals a considerable reduction of temperature is produced. Should

the temperature then be over 60 deg. F., ice must be used, not in the solution, but roughly broken up and mixed with salt in an outer vessel. If ice is placed in the bichromate bath allowance must be made by keeping out part of the water. The ice should be encased in several thicknesses of fine muslin to prevent the solid impurities it generally contains getting into the solution. When recrystallized bichromate is not procurable, a few drops of liquid ammonia added to solution of crude bichromate is recommended. As bichromate is cheap, a fresh solution should be made for each large batch of tissue.

PRINTING THE NEGATIVE.

Any negative that will yield a thoroughly good albumen print is suitable for carbon work. The thinner negatives now made for P.O.P. and similar processes are less satisfactory for direct prints in carbon, for enlargements and reproductions such negatives can be made to yield most satisfactory results by modifying the transparency and the enlarged or reproduced negative. The latitude in this direction is great. No matter how flat the original negative may be, _if all the grades are present_ it can be manipulated in such a way that the most brilliant result will be produced.

PREPARATION OF THE NEGATIVE FOR PRINTING.

The negative is prepared for printing as in all other processes by removing all defects such as pinholes, streaks, etc. For the carbon process the negative requires to be further provided with what is termed a "_safe edge_;" this is a line of black varnish, from one-eighth to half an inch in width according to the sizes of the negatives, painted on its margin, either on the film or glass side. In the case of original negatives masks of opaque paper are used instead of the painted edge, the masks having openings cut in them slightly less than the size of the negative. The purpose of the safe edge is to secure a margin on which light has not acted, as such a margin gives greater freedom to the operator in the process of development by preventing the more deeply printed portions of the picture leaving the support when the backing paper is removed.

DOUBLE TRANSFER PRINTING.


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