HOW TO SUCCEED AT SILK-SCREENING

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SOLAR DEVELOPING

The photofilm material employed in silk-screening consists of a chemical emulsion spread on acetate backing. To expose it, you just make an "open-face sandwich" as follows: First, find a flat board and cover it with white paper for backing. Follow that with the photofilm, emulsion side down. Next, place your film positive (set it so the design is backwards when viewed from above), and—finally—top the stack with a sheet of glass to hold the layers in place (see Photo 2).

Then, when you want to expose your film, cover the "sandwich" with cardboard and carry it into the sunlight. The exposure time will begin as soon as the cardboard is lifted, but will vary with the type of film used. (I've found that Ulano Super Prep or Blue Polybrand films need about 1-1/2 minutes of exposure in direct, midday sun. If—instead of sunlight—you use a Number 2 blue photoflood bulb suspended 18 inches above the glass, however, you should allow 12 minutes.)

Next, the film is developed —emulsion side up—in a tray containing one part hydrogen peroxide and two parts water. (Rock the tray gently throughout the 90-second development period.) The damp emulsion is easily damaged if touched, so —when you move the stencil from the developer to a dry tray—be careful to touch it only by its backing.

Soft portions of the stencil—those that were under the dark areas of the positive —can now be "washed out" with a gentle spray of warm water. This operation takes several minutes, and no harm will come if you overwash the stencil. The step will be complete when the design portions of the positive are totally clear, as shown in Photo 3. To finish the wash cycle, chill the stencil in cool water for at least half a minute.

Now place the design—emulsion side down—on the outside of the screen (Photo 4). Gently wipe any water droplets from the stencil backing, then turn the screen over on a pad of newspapers and blot the inside of the screen with paper towels until a bit of the stencil color comes through (Photo 5). This dabbing must be done carefully, however, since too much pressure will mash the stencil ... while too little can prevent the design from adhering to the screen.

When the stencil has been blotted in place, weight each corner of the screen with a book or other heavy object for half an hour, then stand the screen up vertically overnight. Once the stencil is totally dry, you can—gently—peel off the acetate backing (Photo 6). But don't try this too soon, or you'll pull the stencil off, also.

To get the "press" ready for printing, spread glue blockout (or a water—soluble adhesive such as Le Page's) over all of the screen that's not covered by the stencil, as you see in Photo 7. When the glue is dry, hold the screen up to a light and examine it for unblocked pinholes. Apply more glue if you see any uncovered areas.

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