collotype

photomechanical printing process that gives accurate reproduction because no halftone screen is employed to break the images into dots. In the process, a plate (aluminum, glass, cellophane, etc.) is coated with a light-sensitive gelatin solution and exposed to light through a photographic negative. The gelatin is hardened in exposed areas and is then soaked in glycerin, which is absorbed most in the non-hardened areas. When exposed to high humidity, these areas absorb moisture and repel the greasy ink. The hardened areas accept the ink, and the plate can be used to print a few thousand copies of the positive image.

These methods include serigraphy, collotype, flexography and various mechanical processes used by people who are not trained as printers. Serigraphy, also known as silk-screen printing, is essentially a stenciling process that transfers an image onto a surface. The operator stretches a fine-mesh screen over a frame, outlines the design or text to be printed, and covers the rest of the screen with gum. A squeegee is used to force ink through the uncovered screen; the ink forms small droplets that are deposited evenly on the surface of the printed material. Serigraphy is commonly used to print on cloth, particularly cotton T-shirts.

Tests have determined that people generally feel best under certain temperature, humidity, and air velocity conditions. Temperatures can range from 71° F (21.5° C) with 70 percent relative humidity to 83.5° F (28° C) with 30 percent relative humidity. Relative humidity is the amount of moisture in the air at a specific temperature compared with the amount it could hold at that temperature. Agreeable air velocities range from 15 to 35 feet (4.5 to 10.5 meters) per minute. It is also desirable that an air conditioner remove dust, pollen, smoke, and odors from the air.