This happens to be the trickiest part of the screen printing process due to the number of variables that can affect the exposure.

 After gaining more experience, I realized I had a lot of trouble because I kept changing the variables (i.e. different emulsion types/brands, using vellum vs. transparency film, changing printers with different black ink deposits on the film, changing exposure light sources, artwork that was very detailed versus solid areas, changing the ink types, changing the substrate, etc). My advice is to get solid with a single process first, then learn as you change one variable at a time. The hop-skip-jump method will only lead to frustration and lot’s of wasted time and materials. Trust me, I learned the hard way.

Be patient, be diligent and persevere! Once you get the process down, your results will remain consistent as long as you follow the same steps and your equipment/materials stay intact.            

There are many ways to expose a screen. Any light source containing UV light between 350 and 420 nanometers can expose a screen. Some people even use sunlight (which happens to contain a fair amount of UV radiation). This post will assume you have a bottom-up light source already built (i.e. home-made exposure unit or professional unit). 

Step 1 -  In light-safe conditions, p lace your film positive(s) right side up onto the glass of  your exposure unit. The film positives should appear exactly as you intend them to be printed (not reversed). I tend to place my artwork directly in the middle and away for the very edges of the exposure unit. 

Step 2 – Place your coated screen (completely dry) print side down onto the film positives. Be sure to center the film positives, leaving at least 2-3 inches of room around the designs. Next, place a piece of foam (cut to the inside dimensions of the screen frame) inside the screen frame. If you want to be extra careful about light diffusion, you can fit a black t-shirt over the foam before placing it into the screen. The film positive should be in between the glass and the screen mesh after this step.

Step 3 - On top of this, add some weighted books or anything that will distribute a even amount of pressure and ensure that the artwork and emulsion have great contact with the glass.

Step 4 - Turn off all other lights and then turn on the exposure unit (or if it has a built in timer, set it to the correct amount). Depending on your emulsion type, mesh count, UV tube wattage and artwork, exposure times may vary. You may have to do this step a few times to determine the exact exposure time.

Using Ulano Dual Cure Direct Emulsion, a 30” x 40” exposure unit with 8 UV tubes (FL30T8/BL350), I typically expose for 2 – 3 minutes using this method for great results. 

Step 5 – After the screen has been exposed, quickly move to the washout area. Use a garden hose and cold water to spray both sides of the screen (this stops the chemical reaction). Continue spraying the screen with water with medium pressure. After some time you will notice the screen starting to “open up”. Once this happens use the hose to gently spray the design areas. Do not stop until all the areas have opened up completely. Do not use a pressure washer to do this step as it may actually remove parts of the emulsion that make up your design.

Step 6 – Throughout the process, hold up the screen to a light in order to see if the screen still has bits of emulsion that still need to be removed. Once you are satisfied you can leave the screen to dry. Also, for thinner lines and detailed work, you may need to be very gentle with the washout process and may actually require less exposure time. In these instances, I would consider drying the screen and then re-exposing to “harden” the emulsion.

Step 7 – Ready to be taped!

Capillary film is emulsion that is adhered to a clear plastic film in the form of a roll or a sheet. The film is applied directly to wet mesh. The capillary action (hence the name) causes the emulsion to stick to the mesh. When the frame is ready for use, the plastic film is peeled off, leaving the emulsion intact and ready to expose. The benefit of using capillary film is no nasty emulsion mess to clean up! It does tend to be more expensive though and must be ordered in bulk rolls or sheets.

Capillary film needs lots of water to stick to the screen. Insufficient water leaves air bubbles trapped between the mesh and capillary film that look like white spots. Using a spray bottle filled with water you can dampen the print side of the screen mesh.

This tutorial will go through the step by step process of applying capillary film to your screens. One thing to note – capillary film tends to break down faster when using water-based inks. It should be good for up to a run of 50 prints using a water-based ink system. I use a brand of capillary film called Magna/Cure manufactured by Chromaline.

Step 1 – Open the tube of capillary film in a light safe room.

Step 2 – Measure out the length of film you need for your screen and cut it with a pair of scissors.

Step 3 – After you have degreased your screen, wet it thoroughly. You can also use a spray bottle filled with water. They also selling wetting agents (chemicals) that keep your screen wet and enhance adhesion.

Step 4 - Roll the dull-side of the sheet onto the wet screen’s print side (opposite the squeegee side). You’ll notice the emulsion sticks instantly.

Step 5 – Once the sheet has been spread onto the screen, you may notice some white spots or bubbles. You can use a window washer type squeegee to gently smooth out the sheet. Also, use a spray bottle filled with water on the ink/squeegee side of the screen if there are any dry spots that still need to stick to the mesh. Once the capillary film has been applied to the screen, lay it horizontally in a completely dark room and let it dry for an hour. Use a fan to speed up this process.

Step 6 – Once the screen has dried completely, simply peel the plastic backing when you are ready to expose.