Photographic silkscreen printing uses a light-sensitive emulsion on a mesh screen to transfer a stencil of an image, allowing ink to pass through only the open areas to create a print. Here's a detailed breakdown of the process:
1. Screen Preparation
- Mesh Selection: A fine mesh, usually made of polyester, is stretched tightly over a frame. The mesh count (threads per inch) determines the detail level achievable in the print.
- Degreasing: The screen is thoroughly cleaned and degreased to ensure proper emulsion adhesion.
- Emulsion Coating: A light-sensitive emulsion is applied evenly to the screen using a scoop coater. This is done in a darkroom or a room with safelighting, as the emulsion is sensitive to UV light.
2. Image Creation (Film Positive)
- Artwork Preparation: The image to be printed is created digitally and printed as a film positive – a transparent sheet with opaque areas representing the design. This can be done using a laser printer and transparent film. The opacity of the black areas is crucial for blocking UV light during exposure.
3. Exposure
- Film Placement: The film positive is placed directly onto the emulsion-coated screen.
- Exposure to Light: A UV light source (e.g., a UV exposure unit) is used to expose the screen with the film positive in place. The UV light hardens the emulsion in the areas not blocked by the film positive. The length of the exposure time is crucial and depends on the emulsion type, light source intensity, and film positive opacity.
4. Washing Out
- Removing Unexposed Emulsion: After exposure, the screen is washed with water. The unexposed emulsion, which was shielded by the black areas of the film positive, dissolves and washes away, leaving open areas in the mesh that form the stencil of the image.
5. Drying and Blocking
- Drying: The screen is allowed to dry completely.
- Blocking (Optional): If necessary, any pinholes or unwanted open areas in the stencil are blocked out using screen filler or tape. This prevents ink from passing through these areas during printing.
6. Printing
- Screen Placement: The screen is placed onto the substrate (e.g., paper, fabric) to be printed.
- Ink Application: Ink is applied to the screen along one edge of the image area.
- Squeegee Action: A squeegee is used to pull the ink across the screen with even pressure. This forces the ink through the open areas of the stencil onto the substrate below.
- Lifting the Screen: The screen is carefully lifted, revealing the printed image.
7. Curing
- Drying or Heat Setting: Depending on the type of ink used, the print is either air-dried or heat-set to ensure the ink adheres permanently to the substrate. This is essential for washability and durability, especially on fabrics.
In essence, photographic silkscreen printing creates a durable stencil using light exposure to transfer a design onto a mesh screen, enabling consistent and repeatable printing.
