A photo emulsion is a light-sensitive coating used in various processes, most notably in photography and screen printing. It's essentially a mixture of light-sensitive crystals suspended in a colloid, typically gelatin. This allows for the creation of images by selectively exposing the emulsion to light, causing a chemical change that forms the image.
Understanding Photo Emulsions
Composition:
Photographic emulsion, at its core, is a fine suspension of insoluble light-sensitive crystals in a colloid, usually gelatin. [Reference: Photographic emulsion is a fine suspension of insoluble light-sensitive crystals in a colloid sol, usually consisting of gelatin. The light-sensitive component is one or a mixture of silver halides: silver bromide, chloride and iodide.] The light-sensitive component is usually silver halide crystals (silver bromide, chloride, and iodide). These crystals react to light, forming a latent image.
Applications:
- Photography: Traditionally, photo emulsion was crucial in film photography. Light exposure created a latent image on the film's emulsion, which was then developed into a visible image.
- Screen Printing: Photo emulsion is widely used in screen printing to create stencils. A light-sensitive emulsion is coated onto a screen; a design is then placed on the screen and exposed to UV light. The exposed areas harden, while unexposed areas remain soluble, allowing for the creation of a stencil. [Reference: Photo Emulsion (used with the accompanying Diazo Sensitizer) is a light-sensitive emulsion used to burn stencils directly into a silk screen for photo...] [Reference: This Instructable covers the standard photo-emulsion screen printing process, which is great for printing text or images with fine detail.]
The Process:
The process generally involves:
- Coating: Applying the emulsion evenly onto a surface (film or screen). [Reference: We prefer to apply two coats of emulsion on the print side and one on the squeegee (ink)side. This is how we coat screens for custom exposures.]
- Exposure: Exposing the coated surface to light, usually through a negative or positive image.
- Development: Washing away unexposed or exposed areas, depending on the type of emulsion and process, to reveal the image.
Types and Brands:
Different photo emulsions exist, each with varying sensitivities and properties. Some popular brands include Speedball, and Jacquard Products. [Reference: I bought a speedball intermediate screen printing kit and used their daizo photo emulsion and it was fantastic...] [Reference: Jacquard Products - Chemicals - Photo Emulsion]
Conclusion
Photo emulsion is a light-sensitive material crucial to various imaging techniques, particularly photography and screen printing. Its use enables the creation of images by selectively exposing it to light.
