Platinotype

paper, water, printing and solution

Page: 1 2 3 4 5 6 7 8

the sort of paper to be selected is unsized photographic, smooth or rough, as supplied from Rives or Saxe or by Steinbach.

Solutions of gum arabic and arrowroot have been found the best substances for holding the sensitized liquid. These are prepared as follows: The arrowroot is kneaded into a paste with a little of the water, and the remainder added whilst boiling, the temperature to be kept up for some minutes. The gum arabic solution is said to give the best effects.

The precise amount of sodium or ammonium oxalate necessary is determined by the color of the solution as the addition is slowly made. By formation of corresponding double salts the brownish gray color it at first assumes will change to a beautiful emerald green, and on a further addition of the salt it begins to get somewhat darker. Immediately this is observed the satura tion is complete, and no more must be added. It should be mentioned that the addition of the sodium or ammonium oxalate should be made in the dark room. The mixture is then shaken up and filtered.

No. 5 gives bluish-black tones, and No. 6 is suitable when a more brownish color is desired. The mixture is well stirred up, filtered through muslin, and prepared from non-actinic light. The coating, drying, and storing of the paper are precisely the same as already described for the ordinary platinotype paper. About ninety minims of the liquid will be required for a piece of paper io x 8 inches.

are two or three methods of printing. By the first the action of the light is continued until all the image has appeared of the same depth of tone as required for the finished print. By the second method the printing is carried out until the image is all quite

visible as a whole, although the most delicate detail in the half-tones still remains wanting. The print is then removed from the printing frame and simply kept in the dark room. After a time, varying from half-an-hour to three or four hours, the print will be found to have completed itself, for the reason that the reduction of the platinum salts once started continues in the dark. Or, instead of laying aside to complete itself, the print may in this state be developed over with a cold solution made up as follows : Saturated solution of sodium carbonate 5 c.c.

Distilled water too c. cm.

until all the finest details which are wanting have appeared. A third method of printing is to continue only as long as with the ordinary platinotype paper, that is to say, until the deepest shadows are distinctly visible. The image can then be developed with any of the ordinary pla tinotype developing solutions.

The prints (by whichever of the methods given above they are obtained) are placed in a dilute acid bath made up with— Hydrochloric acid i c.cm.

Water 8o c.cm.

and allowed to remain there until the yellow color of the paper has disappeared. They are then washed for from ten minutes to a quarter of an hour in several changes of clean water.

Page: 1 2 3 4 5 6 7 8