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,5 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 colour added later in the form of chemical toning or dyes.6 The dyes were applied in thin coats so as not to obscure the fine photographic detail. Multiple colours could be used to create the impression of a full-colour image. The skill with which the colours were applied ranged greatly from large blobs of colour 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 colour 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-coloured graphic designs.