Exposing a Screen w/Photo Emulsion

Exposing a Screen w/Photo Emulsion

Using a hand cut stencil on a blank screen as your silk screening method is great for most people. You have a blank space to work with, so you can literally do anything that fits into your printable area. But if you notice you’re using a certain stencil a lot, over countless separate occasions, you’ll save so much time if you toss your plastic/cardboard outline and go for something a little more permanent instead. You can either lay a stencil under the mesh and paint all the negative space in with screen filler, or go the photo emulsion route. Personally, I prefer the latter because it’s way quicker.

You will need:

  • photo emulsion
  • sensitizer
  • squeegee
  • push pins
  • light source
  • clear packing tape
  • dark space
  • acetate sheet(s)
  • newspaper
  • black bristol board

  1. Ignore my complete lack of it in the photo, and lay down newspaper over your work area. This stuff is basically glue, the process can be quite messy, and it’s not easy to clean off of any surface.
  2. Mix your sensitizer into the photo emulsion. The dark green and bright blue will meld together into an awesome bright green.
  3. Lightly coat both sides of your screen with an even layer of emulsion paste. Lightly and evenly. I cannot stress this enough. Learn from my mistakes: if it’s thick and inconsistent, chances are it either won’t shoot or it’ll all fall off in the now-way-longer rinsing process.
  4. Push your pins into each corner of the screen bottom (flat side), and lay them on a flat surface in an area that won’t be exposed to light so it can dry. Remember, this stuff is photosensitive – it fixes where the light hits it, so you want to keep the light away from it until you’re actually exposing the screen.
  5. Mark the date 4 months from when you mix the paste on some tape, and put it on the lid before refridgerating. If you’re not going to put it in the fridge, other lengths/environments for the shelf life of sensitized emulsion are 4 weeks at 90°F (32°C), and 8 weeks at 70°F (21°C).
  6. Print or paint your stencil design onto a sheet of vellum/acetate/anything transparent in black. Make sure no light is allowed through your black lines.
  7. Lay the stencil on the screen bottom so it shows the reverse. If you’ve only got one design on the screen, place it in the middle. If you’re shooting multiple on one, try and make sure there’s at least ¾” of blank space around the edge of the printable area. Using clear tape, tape it down so it won’t shift around.
  8. Set up your light source. Ideally you might have a light table or a clamp light with a 150-250W clear incandescent bulb. Not 100% necessary though. If you’re a use-what-you’ve-got type, do what I did: MacGyver a way to pin a lamp upside down to the bottom of an ironing board, and make a crude reflector from a large half circle of white bristol board. With a crazy intense light table, shooting only takes about 5 minutes. A 250W bulb will be about 10-15. With a 150W bulb, it’s 45 minutes. With a standard 60W soft white bulb, three hours is probably best.
  9. Lay your black bristol board down under the light source, then your screen (bottom side up), flip on the light and leave it there for however long is necessary for your bulb. For 8″ x 10″ – 10″ x 14″ frames, you should lay the screen 12″ from the light source. For 12″ x 18″ – 18″ x 20″, do 17″ and an extra 50% of light time.
  10. When your exposure time’s done, turn off the light and remove the stencil. Using lukewarm water, rinse on the screen top (printing area) side using your hands to lightly rub away the emulsion. After a couple minutes, it’ll start to wash out and you’ll be able to see through the design. You may need to alternate which side you’re rinsing, but don’t spend too much time on the bottom side – it could get over-saturated and the emulsion might start to peel off.
  11. Give your screen one final rinse with cold water, and leave it to dry.

Mind the constant change with stencils in the pictures – the first half were shot with my horrendous failures of overly-coated screens, and the second half were done around midnight when the lighting wasn’t great and I was too frustrated to reshoot the pictures at a later date.

Pretty much the only challenging part of doing photo emulsion is getting the right thickness to the coating. It might take you a few failed attempts and botched screens to get it right, so don’t feel bad if that happens. And don’t coat 4 screens in one go thinking you did it perfectly after two years of not doing so and not bothering to refresh yourself on the process. That’s just asking to spend 2 hours scrubbing emulsion off your screen because you neglected to buy emulsion remover.

Make sure you hold onto your transparent stencil! If you use it enough, your screen will inevitably get too loose and the printing area clogged with old ink, and you’ll need it to shoot a new screen.