Photo emulsion

Photo emulsion is 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.

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Most commercial photo emulsion products consist of either bichromated gelatin or a photopolymer such as bichromated polyvinyl alcohol (PVA) in suspension. It is often light brown in color and has the consistency of heavy syrup. Most brands/types of emulsion 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 emulsion is commonly used in contemporary art to transfer photographs to canvases or other objects.