Keeping pace with the improved methods and machines employed in typographic printing, and influenced thereby, the lithographic and kindred branches of printing have also made progress, induced mainly, however, by the general striving for more rapid and economical production. This has been accomplished by using larger stones, paper and machines, and by employing rotary machines for some work. The use of curved stones for lithography being impracticable for many reasons, a substitute was found in plates or sheets made of zinc or aluminum, which, when properly prepared, possess properties akin to those in lithographic stones. Being flexible, these sheets are easily stretched over the curved surface of a cylinder. Although the development of this branch of printing is due, chiefly, to the French and Germans, much has been done in this country toward its improvement, and work is produced upon Rotary Zincographic or Aluminum Presses that compares favorably with that produced from stones, and at double the speed. The smaller of these presses, printing only one color at a time, prints on sheets 30 × 44 inches, at a speed up to 2,000 impressions per hour; the larger presses of the same kind print on sheets 44 × 64 inches, at a speed up to 1,700 impressions per hour, although the machines may be run even faster, according to the dexterity of the feeder. [Illustration: TWO-COLOR ROTARY ZINCOGRAPHIC OR ALUMINUM PRESS] Two-Color Rotary Presses are in successful operation in different parts of this country. In these machines there are two plate cylinders and one impression cylinder, each of the plate cylinders having its own inking and dampening appliances. The sheet of paper, after being fed to the grippers of the impression cylinder, receives one printing from the first plate cylinder, and a second printing, in a different color, from the second plate cylinder, and is then released from the grippers and delivered in the usual manner by the sheet flier. The size of the sheets printed is 44 × 64 inches, and running at a speed of 1,700 revolutions per hour, the number of printings is 3,400, or double that obtained from the one-color machine of the same size.