Part 127

How Is Photo Engraving Done?

~HOW THE PICTURES IN THIS BOOK ARE MADE~

The first step is the making of the halftone negative which differs from an ordinary negative in being made up of different sized dots instead of shades of gray. This result is obtained by photographing the picture through a halftone screen consisting of two pieces of glass, ruled with black lines and cemented together so the lines cross at right angles and leave small squares of clear glass.

The effect of making the negative in this way is to represent the different shades from black to white by large or small dots. Wet plate photography is usually used in this process because the film is thinner and more intensely black besides being cheaper than dry plates.

New Process Engraving Co.

This cut shows a portion of a halftone cut enlarged so that the dots can be seen very plainly.]

Having made the negative the next step is to make a printing plate from it. To do this, a piece of metal, copper if the work is fine, and zinc for coarser work, is coated with a solution which is sensative to light, fish glue is commonly used to which is added a small amount of ammonium bichromate. The metal being coated and dried, it is put in a very strong frame with the negative and squeezed together so that they are in perfect contact. A powerful light is now directed upon the negative with the metal behind it, the result being that wherever the light goes through the white spaces in the negative, the coating on the metal is rendered insoluble. Where the dots on the negative are, the light is unable to get at the coating so that when the metal is removed from the frame and thoroughly washed this part of the coating washes away, leaving the part which the light got at attached to the metal. This is now heated until the enamel, as the coating is called, turns dark brown and the picture can be easily seen.

The picture is now on the metal but it must be made to stand out in relief before it can be used for printing from, so it is put in a bath of acid which eats away that part of the metal left uncovered by the washing away of the coating and this leaves the dots which make up the picture standing up in relief. A roller covered with very thick paste-like ink is now rolled over the picture, or cut as it is now called, and when a piece of paper is pressed against the ink covered cut each little dot leaves a mark of ink on the paper the total making up the picture as we see it.

There are many more wonderful things connected with the making of cuts such as the routing machine which has a tool that revolves so fast that it turns around 300 times while the clock ticks once, and other machines which cut hard metal as easily as you can cut a potato with a knife.

Colored pictures are also made by the process outlined above. The picture is photographed three times with a different colored piece of glass in front of the lens, the result being three negatives, one of which has all the blue, one all the red and the other all the yellow in the picture. By making cuts from each negative and printing them on top of one another in yellow, red, and blue, the original picture is reproduced in all its colors. This is how all our pretty magazine covers are made.

ACKNOWLEDGMENT

The Editors of the Book of Wonders make acknowledgment herewith to the following. All mentioned have been a great assistance in making the book not only possible but authentic:

Spencerian Pen Co. Eastman Kodak Co. American Telephone & Telegraph Co. Remington Arms Co. Bethlehem Steel Co. American Portland Cement Manufacturers Assn. Brainerd & Armstrong Silk Co. Corticelli Silk Co. Curtiss Aeroplane Co. U. S. Beet Sugar Industry. Hartford Carpet Co. Haynes Automobile Co. Jacobs & Davis, Engineers. Pennsylvania Railroad Co. Endicott, Johnson & Co. United Shoe Machinery Co. Sherwin-Williams Co. Pittsburgh Plate Glass Co. The Colliery Engineer. Lake Torpedo Boat Co. Western Union Telegraph Co. New York Edison Co. Westinghouse Lamp Co. Consolidated Gas, Electric Light and Power Co. of Baltimore. Browning Engineering Co. The White Star Line. Marconi Wireless Co. Plymouth Cordage Co. American Woolen Co. The Vitagraph Co. The B. F. Goodrich Co. The Goodyear Rubber and Tire Co. The Lexington Chocolate Co. The Hecker-Jones Milling Co. The White Oak Mills. The H. C. White Company. A. I. Root Company. Kohler & Campbell. Browne & Howell Co. P. & F. Corbin. Otis Elevator Co. Scientific American. Joseph Dixon Crucible Co. Homer W. Laughlin Co. S. D. Warren & Co. C. B. Cottrell & Sons Co. Mergenthaler Linotype Co. J. F. Tapley & Co. New Process Engraving Co. Mutual Film Corporation. Tobacco Trade Journal Co. McClure’s Magazine. James Arthur. Seth Thomas. American Locomotive Co. New York Central Railroad Co. Columbia Rope Co. Carl Werner. National Wool Growers Assn.

INDEX

=Acid=, carbonic, what it is, 509

=Aerial=, on ship, (illus.), 455

=Aeroplanes=, English Channel crossing (illus.), 132 Curtiss biplane (illus.), 131 first demonstrations of, 130 first flight in Europe, 129 first man-carrying (illus.), 128 first successful (illus.), 126 gas motors used in, 130 gliding, 137 greatest present value of, 136 records of, 131 red wing (illus.), 131 what two brothers accomplished for, 130 Wright Bros.’ inventions, 130

=Age=, why do we, 196

=Air=, does it move with the earth? 400 does it weigh anything? 398 dust in, 38 extend, how far does, 243

=Airlocks=, description of in tunnel building, 213

=Ammunition=, first invention of, 40 fixed, 47 in prehistoric times, 40

=Animals=, can they think? 194 is man an, 180 that leap greatest distance, 122 which foretell weather, 240

=Anthracite seams= (illus.), 260

=Aqueduct= (illus.), 505

=Are= matches poisonous, 294

=Armor=, in the Middle Ages, 44

=Army=, wireless in the, 448-451

=Are= there two sides to the rainbow? 254