Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Photographic Screen Making
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Photographic Screen Making
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Subject: Printing Craft Practice
Class: Senior Secondary 2
Term: 1st Term
Week: 5
Theme: Screen Printing
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Prepare a screen using silk or or gandie. Expose the screen with gelatin solution in sunlight. Make a complete photographic stencil.
completely in a dust-free environment.
Stage 2: Emulsion Preparation and Coating
1. Emulsion Mixing (if applicable): If using a two-part diazo emulsion, mix the sensitizer with the emulsion base according to the manufacturer's instructions. Allow it to de-gas (settle) for a few hours before use to prevent air bubbles. Handle in a dark room or under safe light.
2. Emulsion Application (Coating): Pour a small amount of prepared emulsion into the coating trough. Place the screen upright, resting against a stable surface. Using the coating trough, apply an even, thin layer of emulsion to both sides of the screen.
Method: Start with the print side (underside), applying an even stroke from bottom to top. Flip the screen and repeat on the squeegee side (top side). Multiple coats (1-2 per side) may be applied for thicker stencils, allowing drying between coats. The goal is a smooth, uniform layer without streaks or drips.
3. Drying the Coated Screen: Place the coated screen horizontally, print-side down (mesh touching nothing), or in a vertical drying rack in a completely dark, dust-free room. Allow it to dry naturally or use a fan/hair dryer on a cool setting to speed up the process. Heat can pre-expose the emulsion. The screen must be bone dry before exposure. Any moisture will lead to poor stencil quality.
Stage 3: Artwork Preparation and Exposure (Performance Objective 2)
1. Artwork (Transparent Positive): Ensure the design is completely opaque black on a transparent background. Black areas will block UV light. The artwork should be sized correctly for the screen and print area. For multi-colour designs, separate positives are needed for each colour.
2. Exposure Setup: Once the screen is completely dry, take it to the exposure area. Place the transparent positive (artwork) directly onto the print side (underside) of the screen, right-reading (as you would read it). Secure it with tape to prevent movement.
For Sunlight Exposure: Place the screen (with the artwork facing up towards the sun) on a flat, dark, non-reflective surface (e.g., a black board or cloth). Alternatively, place a sheet of clear glass or plexiglass over the artwork to ensure good contact between the positive and the emulsion-coated mesh. This prevents light from "creeping" under the design, which can cause blurry edges. Expose the screen to direct, strong sunlight. The ideal exposure time varies greatly depending on sun intensity, emulsion type, and mesh count. This requires experimentation (e.g., start with 30 seconds to 2 minutes and adjust). Over-exposure will harden the image area, making it difficult to wash out. Under-exposure will cause the stencil to break down during printing.
For UV Exposure Unit: Follow manufacturer's instructions for exact timing.
3. Exposure: Carefully monitor the exposure time.
Stage 4: Wash-out and Stencil Completion (Performance Objective 3)
1. Initial Rinse (Pre-wash): Immediately after exposure, take the screen to a wash-out booth or a sink. Gently rinse both sides of the screen with cool water. This softens the unexposed emulsion. Do not scrub.
2. Washing Out the Image: Using a medium-pressure water spray (e.g., from a hose nozzle or spray gun), direct the water at the areas where the design was. The unexposed emulsion in these areas will dissolve and wash away, revealing the open mesh of the stencil. Continue spraying until the image areas are completely clear and open. Hold the screen up to a light source to check for clarity.
3. Final Rinse and Drying: Once the image is completely washed out, rinse the entire screen again to remove any loose emulsion residue. Allow the stencil to dry completely. A fan or hair dryer on a cool setting can be used.
4. Spotting/Touch-up: Inspect the dried stencil for any pinholes (tiny unwanted openings) or areas where the emulsion might have chipped. Use a small brush and a little extra emulsion (or block-out fluid) to fill these imperfections. Allow the touch-up areas to dry completely.
5. Hardening (Optional but Recommended): Once dry, some emulsions benefit from a post-exposure to sunlight or a entire screen again to remove any loose emulsion residue. Allow the stencil to dry completely. A fan or hair dryer on a cool setting can be used.
4. Spotting/Touch-up: Inspect the dried stencil for any pinholes (tiny unwanted openings) or areas where the emulsion might have chipped. Use a small brush and a little extra emulsion (or block-out fluid) to fill these imperfections. Allow the touch-up areas to dry completely.
5. Hardening (Optional but Recommended): Once dry, some emulsions benefit from a post-exposure to sunlight or a dedicated hardener to increase stencil durability, especially for long print runs or water-based inks. The complete photographic stencil is now ready for printing. --- Photographic screen making, also known as photo emulsion screen making, is a method of creating a stencil on a screen printing mesh using light-sensitive chemicals. When exposed to ultraviolet (UV) light, these chemicals harden. Areas blocked from light by a design on a transparent film remain soft and can be washed away, leaving an open stencil through which ink can pass. 2.1 Essential Materials and Tools: Screen Frame: Typically wooden or aluminium, stretched with mesh.
Mesh Material: Silk: Traditional, durable, but can be expensive and prone to degradation.
Organdie: A fine cotton fabric, more affordable and readily available in Nigeria, suitable for basic work but less durable and precise than silk or polyester.
Polyester Mesh (Monofilament): Modern, synthetic, highly durable, stable, and offers excellent detail retention. Available in various mesh counts (e.g., 80-120T for textiles, 150-200T for fine details on paper/plastic).
Photo Emulsion (Gelatin Solution): A light-sensitive liquid that forms the stencil. Commonly, this is a direct emulsion system.
Diazo-based Emulsion: Two-part system (emulsion base + diazo sensitizer). Offers good durability and detail.
Photopolymer Emulsion: One-part system, ready to use, faster exposure times, excellent detail, and durability. Dichromate-based Emulsion (e.g., Potassium Dichromate with PVA or gelatin): A traditional, cost-effective, but less stable and more hazardous option sometimes used in resource-constrained environments. For this lesson, "gelatin solution" will refer to any suitable photopolymer or diazo emulsion commonly used, with a practical emphasis on readily available options.
Coating Trough (Scoop Coater): Used to apply an even layer of emulsion to the screen.
Degreaser: A chemical cleaner to remove oils and contaminants from the mesh, ensuring good emulsion adhesion.
Transparent Positive (Artwork): A clear film or transparency with the design printed in opaque black. This blocks UV light during exposure. Can be made from tracing paper, acetate sheets, or professionally printed films.
Exposure Unit/Light Source: Sunlight: A common and free UV source in Nigeria. Requires careful timing and consistent intensity.
UV Exposure Unit: Controlled environment, consistent light, faster exposure times.
Halogen Work Light: Some teachers might use this as a makeshift UV source, though less efficient than dedicated UV lamps.
Wash-out Booth/Spray Gun: For washing away unexposed emulsion. A water hose with a spray nozzle can suffice.
Dark Room/Safe Light: For handling emulsion and drying the coated screen before exposure.
Tape: For blocking pinholes and edges.
Squeegee: For applying ink during printing (though not directly used in stencil making, it's part of the screen printing process).
Fan/Hair Dryer: To aid in drying the emulsion and stencil. 2.2 Step-by-Step Process of Photographic Screen Making: Stage 1: Screen Preparation (Performance Objective 1)
1. Frame Inspection: Ensure the screen frame is sturdy, clean, and free from warps.
2. Mesh Stretching: Place the chosen mesh (silk or organdie) over the screen frame. Starting from one side, staple or glue the mesh tightly to the frame. Carefully stretch the mesh across the frame, ensuring uniform tension in all directions. Use stretching clamps if available, or manually pull and secure opposite sides sequentially (e.g., top, bottom, then left, right) to achieve a taut, wrinkle-free surface. Proper tension is critical for good print quality. Trim excess mesh.
3. Degreasing: Thoroughly clean both sides of the stretched mesh with a degreaser solution (or a mild dishwashing soap solution, followed by extensive rinsing). This removes oils, dust, and contaminants that can prevent the emulsion from adhering properly. Rinse the screen thoroughly with water until all degreaser residue is gone. Allow the screen to dry completely in a dust-free environment.
Stage 2: Emulsion Preparation and Coating
1. Emulsion Mixing (if applicable): If using a two-part diazo emulsion, mix the sensitizer with the emulsion base according to the manufacturer's instructions. Allow it to de-gas (settle) for a few hours before use to prevent air bubbles. Handle in a dark room or under safe light.
2. Emulsion Application (Coating): Pour a small amount of prepared emulsion into the coating trough. Place the screen upright, resting against a stable surface. * Using the coating trough, apply an even, This section outlines the pedagogical steps for delivering the lesson, emphasizing practical demonstration and active student participation.
Teacher Activities: Introduction & Review (10 mins): Introduce "Photographic Screen Making" as a method for precise design transfer in screen printing. Briefly review the basic principles of screen printing and the need for a stencil. Display various printed items (t-shirts, posters) and discuss how intricate designs require this advanced technique.
Key Concepts Explanation (15 mins): Define photographic screen making and its advantages over manual stencil cutting.
Explain the function of each material: screen mesh, emulsion, transparent positive, light source. Emphasize the role of UV light and light-sensitive chemicals.
Demonstration: Screen Preparation (Performance Objective 1) (20 mins): Demonstrate how to properly inspect a screen frame.
Practical Demo: Show the correct technique for stretching silk or organdie mesh onto a frame, ensuring proper tension. (If facilities allow, students can observe closely or assist).
Practical Demo: Demonstrate degreasing the screen with the appropriate solution and rinsing thoroughly. Show how to check for dryness.
Demonstration: Emulsion Coating & Drying (15 mins): Practical Demo: Show how to mix a two-part emulsion (if applicable) or prepare a one-part emulsion. Stress working in low light/dark room.
Practical Demo: Demonstrate coating the screen evenly using a coating trough, explaining the importance of thin, uniform layers. Apply 1-2 coats per side. Explain the importance of drying the coated screen completely in a dark, dust-free environment. Show a prepared drying rack.
Demonstration: Exposure Setup (Performance Objective 2) (20 mins): Display examples of transparent positives and explain their characteristics (opaque black design, clear background).
Practical Demo: Position the transparent positive onto a pre-coated, dry screen.
Practical Demo: Demonstrate the setup for sunlight exposure: placing the screen on a dark surface, positioning the positive, and covering with glass for contact. Discuss varying exposure times based on sun intensity and emulsion type. If sunlight isn't available/reliable, simulate with a UV lamp or strong halogen light, explaining the principles.
Demonstration: Wash-out and Stencil Completion (Performance Objective 3) (20 mins): Practical Demo: Demonstrate the gentle pre-rinse.
Practical Demo: Show how to use a water spray to wash out the unexposed emulsion, revealing the stencil. Guide students on checking for clear image areas against light.
Practical Demo: Demonstrate final rinsing and drying.
Practical Demo: Show how to inspect for pinholes and perform touch-ups using emulsion or block-out. Explain the optional post-hardening process.
Discussion and Q&A (10 mins): Facilitate a class discussion on common challenges (e.g., under/over exposure, uneven coating, pinholes) and troubleshooting. Answer student questions.
Assignment: Assign relevant practical or theoretical tasks for students to prepare for the next lesson.
Student Activities: Active Observation & Note-Taking: Students will attentively observe all demonstrations, taking detailed notes on materials, procedures, and safety precautions.
Q&A Participation: Students will actively ask clarifying questions during and after demonstrations.
Group Discussion: Participate in class discussions, sharing observations and potential challenges. Simulated Practice (if actual practice is limited): Students can simulate stretching mesh, coating a frame (without emulsion), and positioning artwork on a dry screen.
Material Identification: Identify various mesh types, frames, and tools used in photographic screen making.
Artwork Preparation (Homework): Design and prepare a simple black-and-white transparent positive for future use (e.g., drawing on tracing paper with opaque marker). ---
This topic holds significant practical and economic relevance in the Nigerian context. Entrepreneurship in Textile and Garment Decoration: Photographic screen making is the cornerstone for customized apparel printing. Many small and medium enterprises (SMEs) in Nigeria rely on this technique to print designs on t-shirts, caps, uniforms for schools and businesses, and traditional attire. Students mastering this skill can start their own print shops, offering custom design and production services for local markets, events, and fashion lines. This directly contributes to job creation and economic empowerment among youth in Nigeria. Advertising, Branding, and Signage: The ability to produce high-resolution, durable stencils allows for the creation of professional advertising materials. Businesses in Nigeria frequently use screen-printed posters, banners, stickers, and outdoor signage due to its cost-effectiveness and durability. Students can integrate into this sector by producing promotional materials for local businesses, political campaigns, and community events, offering an affordable alternative to digital prints for large quantities.
Cultural and Creative Industries: Beyond commercial applications, photographic screen printing is used in Nigeria's vibrant art and craft scene. Artists can use this method to create limited edition prints, designers can produce unique fabric patterns (e.g., modern interpretations of Adire or Ankara), and craftspeople can print on various substrates for decorative items. This integrates the technical skill with cultural expression and supports the creative economy. ---