Photo emulsion screen printing works by coating mesh with light-sensitive emulsion, exposing through your design film, and washing out unexposed areas.
For the full breakdown, see our best Emulsion For Screen Printing guide.
Photo emulsion is the go-to method for creating durable, high-detail stencils on screen printing screens. The process uses a light-sensitive liquid that hardens where UV light hits it and stays water-soluble where your artwork blocks the light, leaving a clean stencil ready for ink. The full sequence takes about an hour of active work plus drying time, and most results come down to getting the coat thin and the exposure right.
What You Need to Get Started
The basic setup includes a mesh screen (thoroughly degreased), photo emulsion with its sensitizer for diazo or dual-cure types, a scoop coater or squeegee, a dark drying area, your design on transparent film, a UV light source, screen printing ink, and tape or screen filler for touch-ups. The emulsion you pick affects exposure time and how long the stencil lasts — for help choosing the right option, check out our roundup of the best emulsion for screen printing to match your project needs.
The Step-by-Step Process for Using Photo Emulsion
Each step in the sequence matters — rushing or skipping will show in the final print.
1. Clean the screen. Grease, dust, or residue prevents emulsion from bonding. Use a dedicated degreaser on both sides and let the screen dry completely.
2. Mix the sensitizer. For diazo and dual-cure emulsions, fill the sensitizer bottle about three-quarters full with cold water, shake until dissolved, then pour it into the emulsion and stir until the color is uniform.
3. Coat both sides evenly. Lay the screen flat with the bottom side facing up. Pour a bead of emulsion across the bottom of the mesh. Pull the scoop coater upward in one smooth, steady pass. Flip the screen and repeat on the other side. The coat should be thin and even — thick layers cause poor resolution and difficult washout.
4. Dry in total darkness. Place the coated screen in a light-safe cabinet or dark room. Elevate it with pushpins or blocks so air circulates under and over it. Dry for at least 45 minutes, or overnight if needed. The emulsion must be completely dry before exposure.
5. Expose with your artwork. Place your transparency (laser prints hold up best) against the flat side of the dry coated screen. Hold it flat with a piece of clean glass or an exposure unit. Shine a UV source — a dedicated exposure unit, a 150W bulb, or direct sunlight — onto the assembly. Exposure times vary by mesh, coating, and light source; run an exposure test strip to find your correct time.
6. Wash out the stencil. Spray the screen with cool or lukewarm water. The unexposed emulsion under the dark areas of your film washes away, leaving your design open. If nothing washes off, the screen is overexposed and you will need to start again with less exposure time.
7. Patch and seal. Once the screen is dry, inspect the stencil for tiny pinholes. Fill them with screen filler, and tape the edges of the screen to prevent ink from leaking around the frame during printing.
8. Print and heat-set. Place the screen over your fabric, lay a line of ink across the top of the design, and pull it across the mesh with a squeegee at a 45-degree angle. After printing, heat-set the ink per the manufacturer’s directions — this usually means ironing on high for several minutes.
Common Screen Printing Problems and Their Fixes
Even experienced printers run into these issues occasionally. The table below covers the most frequent problems and how to resolve them.
| Problem | Likely Cause | How to Fix |
|---|---|---|
| Emulsion won’t stick to mesh | Screen is greasy or dirty | Degrease thoroughly before coating |
| Stencil lacks sharp detail | Coating is too thick | Apply thinner, more even coats |
| Image won’t wash out | Screen was overexposed | Reduce exposure time on the next run |
| Stencil washes away completely | Underexposed | Increase exposure time or check transparency density |
| Pinholes in the stencil | Dust on screen during coating | Clean screen and work area before coating |
| Emulsion cracks during drying | Coating too thick or dried too fast | Apply thinner coat and dry at room temperature |
| Ink bleeds under the stencil | Stencil not fully sealed at edges | Tape screen edges and patch all pinholes before printing |
Once you dial in your timing and coating consistency, photo emulsion delivers crisp stencils that hold up for dozens of prints. Run a test screen first to lock in your exposure window before printing the final run.
FAQs
Can I use an inkjet printer for the transparency?
Inkjet prints can blur or run when the transparency gets wet during washout. Laser printer transparencies hold up much better to the water spray and produce sharper stencils. If you only have an inkjet, seal the print with a fixative spray before exposing.
How do I find the right exposure time?
Exposure time varies with mesh count, coating thickness, emulsion type, and light source distance. Use an exposure calculator or a step wedge test strip to determine the ideal time for your specific setup. Testing in short increments and inspecting washout results is the most reliable method.
Why does my stencil have rough edges?
Rough edges usually come from poor contact between the transparency and the coated screen during exposure — light leaks around the edges of the film. Place the transparency directly against the mesh and hold it flat with glass or a vacuum exposure unit for crisp edges.
References & Sources
- Chromaline. “A Beginner’s Guide to Making Screens for Screen Printing.” Covers the full process from cleaning to exposure and washout.
Mo Maruf
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