Photocollography

Photolithography is a method in graphic arts that uses light for etching designs. Often confused with zincography in Greece, it falls under the category of autotype/reproduction.

Characteristics of Photolithography:

• The engraver uses a raster, a grid of dots arranged in parallel horizontal and vertical lines.

• This type of grid was first used by William Fox Henry Talbot (1800-1877) in 1853, but it was first used in a camera by E. and G. Bullock in 1865.

• In 1850, Frenchman Fermin Gillot (1820-1872) created relief plates coated with asphalt to illustrate the Parisian newspaper L'Avant-Scene.

Technique:

• A standard raster consists of two glass plates with parallel lines of dots, which are not visible due to the varnish applied over them.

• The raster, which can be either linear or tonal depending on the nature of the image to be printed as photolithography, is placed in front of the photographic plate.

• The two plates are positioned so that the parallel dots intersect at a right angle, creating dense areas in the shaded regions and sparse areas in the white ones (half-tone photolithography).

Process:

• After the negative photographic image is developed, the positive image is printed onto a zinc plate, which is sensitized with a gelatin glue coating (lepas) containing dichromate salts.

• After printing, the design on the zinc plate is revealed in a violet dye solution, and the plate's bottom surface is heated to enamel the design elements.

• During the subsequent oxidation, a dilute solution of sulfuric or, more commonly, nitric acid corrodes the parts of the zinc plate that were not exposed to light, leaving the design ready for printing.

Color Photolithography:

• In color photolithography, different color areas are photographed separately, with each color printed separately, up to a total of four, and the shades adjusted by hand.

• These colors produce various tonal gradations.

• Later, color films were used in photolithography.