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.
506. Of all the printing processes, especially those best for the busy photographer, there are none offering the advantages of the platinotype, or platinum process. Among pictorial workers and professional photographers no process occupies a more prominent place. For simplicity of manipulation and charming results that yield most pleasing gradations of light and shade, together with a wide range of half-tones of exquisite delicacy, no printing process is more popular than platinum.
Theory Of Process. The manufacture of sensitive platinum paper differs quite materially from gelatin and collodion papers, in that it is not necessary to employ a substance to hold in suspension the sensitive salts, as is the case with the regular printing-out papers. Platinum paper is sensitized by coating a chemically pure paper with a solution of ferric oxalate and potassium chloro-platinite. When exposed to light the ferric oxalate is changed to ferrous oxalate, and the ferrous salt, when in solution has the power to reduce potassium chloro-platinite to metallic platinum. As a solution of potassium oxalate will dissolve the ferrous oxalate, it is employed as the developing agent. After the picture has been developed a permanent image is secured by placing the print in a very weak solution of hydrochloric acid, which removes all chemicals, leaving only the metallic image of platinum.
508. Exposure varies according to the character of the negative and the condition of the light, but, when the exposure is complete the whole process of developing, clearing, washing and even mounting can be accomplished in from fifteen to twenty minutes. Taking into consideration the length of time required to print, wash, tone, fix and finally wash the gelatin and collodion prints, it will be clearly seen that the platinum process is a great time saver. In addition to this, there is no difficulty in securing even tones, no troubles with blisters, stains, discoloration, fading and many of the other difficulties with which the photographer has to content in other processes. Platinum paper possessing a matte surface has a texture which gives the picture an appearance similar to a pencil drawing or engraving.
509. The one important caution which must be observed in handling platinum paper is to keep it perfectly dry, as it is very susceptible to dampness. The lump of calcium chloride in each can should be kept perfectly dry, to insure the paper being properly preserved. Dampness has almost the same action on the iron salts as light. It changes the ferric oxalate to ferrous oxalate. For this reason a damp paper must not be printed as far as a perfectly dry paper, because it will develop up so quickly it will get beyond control and become too dark. Do not print from damp paper. If it is damp dry it thoroughly before printing.
Platinum Paper - Black and White.
Grades Of Platinum Papers. Platinum paper is made in different grades to suit various purposes. For instance, the paper manufactured by Willis & Clements, known as the W. & C. Paper, is made in six different grades: Medium heavy smooth (Labeled B B); heavy smooth (K K); heavy medium rough (T T); heavy rough (C C); extra heavy smooth (Y Y); extra heavy rough (Z Z).
511. Paper manufactured by the American Aristotype
Company is made in five grades, as follows: Heavy smooth (Labeled H S); heavy rough (H R); extra heavy smooth (E H S); extra heavy rough (E H R), and medium rough (ivory tint).
51.2. The Angelo platinum paper is made in two grades, smooth and rough.
513. There are numerous other papers manufactured, but all are manipulated in practically the same manner, the only difference being that some require deeper printing than others; while there are brands which require slower and further development. Warmer or colder solutions are recommended for various papers. The general manipulation in all, however, is about the same, any material change or special manipulation necessary for any particular brand of paper being given in the formula which accompanies each package sent out by the manufacturer. The photographer who has learned to manipulate one grade of platinum paper can generally handle all grades.
514. Platinum paper is a semi-developing out paper, the image being only partially visible when printed.
Printing. For printing, place the paper in a printing frame in the regular way, with the yellow sensitive side in contact with the negative. Print in the sunlight until the half-tones and all detail are visible. As the paper is quite sensitive it should be placed upon the negative and inspected in subdued light during printing.
Fixing. Directly from the developing bath the prints, without rinsing, are immersed in the acid fixing bath, containing 1 ounce C. P. muriatic acid to 60 ounces of water. After all prints are developed they must be given jv - 10 four acid baths, of the same strength as the first bath and then washed by handling over in from four to six changes of clear water. They should then be placed between blotters to dry.
518. Note: The developing salts supplied by the manufacturers are sold in one-half and one pound boxes, mixed in definite proportions, and must all be dissolved at one time, otherwise the tone of the prints will not be uniform.