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Photo EmulsionPhoto 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) is transferred onto a transparent medium such as glass or film which is placed over the emulsed screen. Ultraviolet light is shone 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 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 screenprinting, the emulsion may be stripped from the screen using a chemicals known in the industry as reclaimer, usually one or a number of extremely toxic solvents.
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