Screen Printing Techniques and Tips: Direct Emulsion Stencil Making

Screen printing is a form of direct printing that relies on ink being forced through the openings in a stencil that has been applied over a screen for support. Two main types of stencils are used in modern screen printing techniques: Capillary Film and Direct Emulsion stencils. Our purpose in this article is to examine the latter, direct emulsion stencil making.

Direct Emulsion stencils are frequently chosen for their economy and control. By coating more than one or two passes of the coater onto the screen, a very thick coat of emulsion can be created. Thick stencils allow more ink to be transferred to the garment, a technique desirable for certain special effects inks such as puff and glitter.

Emulsion is a light-reactive compound that changes its properties when exposed to ultraviolet light. A positive of the image (the opposite of a negative!) is made, and held in contact with the emulsion while light is used to expose the emulsion. Areas of the emulsion that receive UV light 'harden' and become relatively insoluable in water. Areas covered by the image to print do not harden, and are rinsed away with a high-pressure spray of water. These areas are now open, and ink can be forced through them onto a garment to print an image!

In order to create a direct emulsion screenprinting stencil, you'll need a screen of the appropriate mesh and tension, a scoop coater or other device to apply emulsion to the screen, and of course, the emulsion. There are three main types of emulsion in use today. They are categorized by the way the emulsion develops:

To apply direct emulsion, prepare it as the manufacturer recommends. All emulsions are light-sensitive and therefore you need to work in a room no brighter than absolutely necessary to see what you're doing. A safelight is preferable, but a nightlight will work. Avoid flourescents and HID lighting as it tends to produce high levels of UV, which quickly exposes your emulsion.

Pure photopolymer emulsions may need no mixing if the dye is premixed, or not needed. Fill a scoop coater if you have one (they quickly pay for themselves!). Tilt the screen so that the shirt side is at a 45 angle to the floor and grasp it firmly in your weak hand. Place the scoop coater at the appropriate angle as indicated by the lands on the end caps, and draw it at a constant rate, in one motion, from bottom to top.

Now position the squeegie side at a 45 angle to the floor and coat it in the fashion you just coated the other side. It is important to end on the squeegie side to produce the best stencil. You may coat the screen three times, even four if you need to - but usually two passes, one on each side, is plenty.

The emulsion will need at least an hour or two to dry. The screen should be stored shirt side down, in the horizontal position, and kept in complete darkness. Coated screens that are dry can be stored vertically, and usually will last at least a month unexposed, if well stored.

To expose the emulsion and make a stencil for printing, any high-UV light source can be employed. If you weren't aware from all those sunblock commercials, the sun is a high-UV light source, and it can be used to expose a screen! It isn't high-tech, but it will work. You can't expect to do fine detail work, but you can make screens for most line art this way.

If you have purchased a light source, suspend it three feet above a flat work surface. Support the area of the screen to be exposed from the squeegie side by turning the screen shirt-side up over a raised surface so that the screen itself and not its frame hold the frame up. You can use a box, phone book, etc. but try to get something solid that supports the screen and keeps it flat.

Position your positive over the emulsion, considering where the image should fall on the garment. The positive should be placed so that it is upside down. In other words, if you were where that box or phone book is, looking through the emulsion with X-ray eyes to see the artwork, it would look just like it will when printed on the shirt.

Use a piece of clear, clean glass to press the positive into firm contact with the emulsion. No need for excessive pressure if you are just doing line work - just keep the positive flat. Fire up the light source and expose your screen!

How long to expose it? That varies greatly based on a number of factors. We know that is not a very gratifying answer, so here is a very general guideline: In bright sunlight, 15 min., 500W Quartz, 10 min., 5KW Xenon 2 min.

Once your image is burned into the screen, direct a high-pressure spray of water into the mesh. We've met printers who very successfully burn screens at home, then bag them in opaque trash bags and take them to the car wash. If you move quickly to get the screens wet and washed out, this will work! A garden hose with a jet nozzle will work, and you can buy sprayers designed for this purpose.

Use the water spray to rinse out the emulsion from the printing areas of the screen. Start on the shirt side for a small benefit to image quality. Let the water do its work and don't worry if it takes several passes, especially if your water source is not as powerful as a car wash.

Blockout. Since you will probably need to fill open areas around the edges of the screen, it is desirable to have a product called blockout. This can be a liquid that is applied and allowed to dry, or a tape that is applied to the mesh. Either way, apply the blockout to the shirt side, and try to make sure you stay at least an inch from the edge of the image.

Upon drying, your stencil is ready to mount in your press!