A little about cinema slides

The current exhibition, Flickering Light, includes a display of old cinema slides, including some for South Taranaki businesses. Here’s some information about slides and how they were made.

A cinema slide consists of an image supported on a glass substrate or base (82mm, 3½ inches square), with a cover glass to protect the surface of the image. The two pieces of glass are held together with gummed paper or cloth tape. Often an aperture mask, cut from high quality black cardboard, is positioned between the pieces of glass. The mask may be cut in a variety of shapes, including square, rectangular, circular or oval or, more rarely, complex silhouettes such as hearts.

Cinema slides with photographic images were produced as duplicates from original or composite negatives. To print the image onto the slide, two methods were commonly employed – contact and optical.

Contact printing uses a frame to hold the emulsions of the negative and slide together in close contact. A light is shone through the negative exposing the emulsion of the slide. The slide is then processed using photographic developer, stop bath and fixer and then washed and dried. Once dry, the slide is mounted with the optional aperture mask and cover glass and then bound together with gummed tape.

The optical printing method exposes the image by projecting the negative, or negatives, onto a slide coated with emulsion. The processing procedure is the same as that used in contact printing.
From the 1850s to the 1960s, most photographic slides were produced in monochrome, with color added later in the form of chemical toning or dyes. The dyes were applied in thin coats so as not to obscure the fine photographic detail. Multiple colors could be used to create the impression of a full-color image. The skill with which the colors were applied ranged greatly from large blobs of color to fine applications with delicate brushstrokes.

During the 1960s and 1970s cinema slides incorporated cut sheets of processed photographic film mounted between two sheets of plain glass, a technique that took advantage of advances in color photography and was cheaper than using layers of glass. The slide dimensions were kept the same to ensure compatibility with existing projection equipment.

While many cinema slides were photographic in origin, others were screen printed, handwritten or typed in ink or paint directly onto the glass substrate or onto materials such as cellophane. The finished product ranged from text or simple line illustrations to sophisticated hand-colored graphic designs.

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