Photo emulsion

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For photographic emulsions used in photographic films and papers, see photographic emulsion.

Photo emulsion is a commonly used misnomer for a photosensitive substance used in screen printing that hardens when subjected to ultraviolet light. To prepare a screen for printing, it is coated with liquid photo emulsion and allowed to dry. Opaque, monochromatic artwork (known as a stencil or a positive) is transferred onto a transparent medium such as glass or film which is placed over the emulsified screen. Ultraviolet light is shown on the screen causing the emulsion to become hard and insoluble, except in areas that are covered by the opaque artwork. The entire screen is then washed in water or solvent, allowing any emulsion not hardened by the light to rinse away, leaving a representation of the artwork on the screen.

Most commercial photo emulsion products consist of silver halides suspended in gelatin such as Liquid Light, but the incorrect usage of this term has been extended to those products which consist of either bichromated gelatin, a solution, or a photopolymer such as bichromated polyvinyl alcohol (PVA), a suspension. It is often light brown in color and has the consistency of heavy syrup. Most brands/types of emulsion or any photo sensitive material have a short shelf life (on the order of days or months) and must be refrigerated.

After being used for screen printing, the emulsion may be stripped from the screen using chemicals known in the industry as reclaimer, usually one or a number of extremely toxic solvents.

Photo sensitive solutions, suspensions or emulsions are commonly used in contemporary art to transfer photographs to canvases or other objects.