If you are just starting out in screen printing, one of the most important steps in the process is exposing your screen properly. Exposure refers to the stage where you use UV light to harden the emulsion on the screen around your printed design, creating a stencil. To get clean, accurate results, it is essential to prepare your setup carefully. One common question from beginners is what exactly should go underneath the screen when exposing it. The right surface beneath your screen helps ensure good contact between the film positive and the emulsion, leading to a crisp and well-defined image.
In this article, we will explain what you should use under the screen when exposing, why it matters, and how to get the best exposure results at home or in a studio.
Why Contact Is Crucial During Exposure
The goal of exposure is to create a sharp stencil by hardening the light-sensitive emulsion on the screen. Any areas that are blocked by the design will wash away later, allowing ink to pass through in those places during printing. For this process to work correctly, the film positive must sit flush against the emulsion-coated side of the screen.
If there is any gap or uneven pressure, light can leak into unwanted areas and cause a blurry or poorly defined image. That is why it is vital to place something underneath the screen that supports the mesh evenly while allowing good contact between the screen and the film.
What to Put Underneath the Screen
The most commonly used surface under the screen during exposure is a black foam pad or black fabric-covered cushion. This should be slightly soft but firm enough to provide even support. The dark colour prevents light from bouncing back into the screen which could affect the unexposed emulsion.
A sheet of black felt, thick black card, or a piece of black-out curtain material can also work well in home setups. These materials help absorb light and reduce reflections which helps maintain cleaner stencil edges.
For DIY exposure setups, some people use layers of black t-shirts, towels, or rubber mats underneath the screen. The key is to ensure that the surface is flat, has a little give, and does not allow UV light to reflect back through the mesh.
Using a Weight or Clear Glass on Top
While the material underneath the screen provides support, you also need pressure from the top to hold the film positive tightly against the screen. Most screen printers use a sheet of clear glass or acrylic placed over the film to ensure direct contact. This weight presses the film down evenly and prevents any movement during exposure.
Make sure the glass is clean, flat and heavy enough to hold everything in place. Do not use tinted or UV-blocking glass as it can interfere with the exposure process.
Positioning Your Exposure Setup
Lay your foam or black cloth flat on your exposure table or workbench. Place the screen face down with the emulsion side resting directly on the film positive which should already be aligned and taped in place. Sandwich the film with the clear glass from above to keep it flat and prevent light leaks around the edges.
If you are using a homemade exposure unit with UV bulbs, make sure the light source is evenly positioned above the screen and at the right distance. Uneven exposure can result in undercooked or overexposed areas of the stencil.
Avoiding Common Mistakes
One of the biggest mistakes in the exposure process is using a shiny or light-coloured surface underneath the screen. Surfaces like white card, glass tables or metal worktops can reflect UV light back into the screen causing partial exposure in the areas that should remain soft.
Also, avoid using overly soft materials that cause the screen to sink or bow during exposure. This can lead to uneven stencils and blurred edges.
If you are reusing materials from other parts of your workspace, make sure they are clean, flat and free from dust or moisture. Dirt or debris under the screen can also distort the image during exposure.
Tips for Better Results
Use a dark-coloured base that absorbs light and provides even support. Make sure your film positive is aligned correctly and held flat by the glass. Test exposure times with a step wedge if you are unsure how long to expose your emulsion.
If you consistently struggle with image sharpness, consider upgrading your exposure unit or switching to a vacuum exposure table which uses air pressure to keep the film and screen tightly pressed together.
Final Thoughts
What you place underneath your screen during exposure plays a major role in how clean and accurate your final print will be. Using a firm, dark, non-reflective surface ensures even contact and prevents light from bouncing back into the mesh. With the right setup and a little care, you can produce sharp and professional-quality stencils that hold up well during printing.