Part 356

A.—Screen Solutions.—

Blue violet.

By weight Methylene blue 5 parts Tetraethyldiamidooxytriphenyl carbinol 2 parts

Or:

By weight Methyl violet 5 parts Alcohol 200 parts Water, distilled 300 parts

Green.

By weight Malachite green 10 parts Alcohol 200 parts Water, distilled 300 parts

{549}

Yellow.

By weight Acridin yellow N. O. 10 parts Alcohol 200 parts Water, distilled 300 parts

Red.

By weight Congo rubin 10 parts Alcohol 200 parts Water, distilled 300 parts

B.—Dyes (Stock Solutions).—

By weight I.—Acridin yellow or acridin orange, N. O. 1 part Alcohol 100 parts Water, distilled 400 parts

By weight II.—Congo rubin 1 part Alcohol 100 parts Water, distilled 400 parts

By weight III.—Tetraethyldiamidooxytriphenyl carbinol 1 part Alcohol 100 parts Water, distilled 400 parts

The screen solutions, after being filtered through paper filters into clean dishes, are utilized to bathe 6 clean glass plates previously coated with 2 per cent raw collodion; we require 1 plate for blue violet, 2 plates for red, 2 plates for yellow, and 1 plate for green, which in order to obtain the screens are combined in the following way: Yellow and red plate, yellow and green plate. For special purposes the other red plate may be combined with the blue violet. Another method of preparing the screens is to add the saturated solutions drop by drop to a mixture of Canada balsam and 2 per cent castor oil and cement the glasses together. Those who consider the screens by the first method too transparent, coat the glass plates with a mixture of 2 to 3 per cent raw collodion and 1 per cent color solution. Others prefer gelatin screens, using

By weight Hard gelatin (Nelson’s) 8 parts Water 100 parts Absolute alcohol 10 parts Pigment 1 part

This is poured over the carefully leveled and heated plate after having been filtered through flannel.

The collodion screens are cemented together by moistening the edges with Canada balsam (containing castor oil) and pressing the plates together in a printing frame, sometimes also binding the edges with strips of Japanese paper.

On the evening before the day of work, good dry plates of about 18° to 24° W. are dyed in the following solution:

By weight Stock solution, No. 1 16 parts Distilled water 100 parts Alcohol 5 parts Nitrate of silver (1.500) 50 parts Ammonia 1–2 parts

This bath sensitizes almost uninterruptedly to line A. The total sensitiveness is high, and the plate develops cleanly and fine. Blue sensitiveness is very much reduced, and the blue screen is used for exposure. As far as the author’s recollection goes, the plate for the yellow color has never been color-sensitized, many operators using the commercial Vogel-Obernetter eosin silver plates made by Perutz, of Munich; others again only use ordinary dry plates with a blue-violet screen. This is, however, a decided mistake, necessitating an immense amount of retouching, as otherwise it produces a green shade on differently colored objects of the print.

For the red color plate the dry plate is dyed in

By weight Stock solution, No. 2 10 parts Distilled water 100 parts Nitrate of silver (1.500) 100 parts Ammonia 2 parts

The resulting absorption band is closed until E, reaching from violet to red (over C). This red pigment was examined by Eder, who obtained very good results, using ammonia in the solution.

The corresponding screen is a combination of malachite green with acridin yellow or acridin orange N. 0.

For the blue color plate the dye is made up as follows: