Silk Screen Printing
 
Silk screen printing is a simple, inexpensive method of producing multiple copies
of attractive visual aids, posters, and other materials, including typewritten pages.
A squeegee forces very thick paint through those parts of the silk screen that
are exposed by the stencil onto paper placed underneath the screen. The silk-screen
process presented here is used for educators and trainers who must
prepare their own training materials. It would require considerable upgrading of
equipment and materials to be appropriate for commercial painting operations.
 
BUILDING THE SILK SCREEN PRINTER
 
                              Tools and Materials
 
Hinges, about 2.5cm x 7.5cm (1" x 3")
Wing or regular nuts
Squeegee
Trigger support
Wood for frame
Baseboard or smooth table top
Silk or other sheer cloth
Thumbtacks
Silk screen paint
Paper for copies
Water-soluble paint, e.g., finger paint
(Oil-soluble paint also works well,
but a solvent is needed to clean it off the screen.)
 
1.  Build a frame (see Figures 1 and 2), using 1.9cm x 5cm (3/4" x 2") plywood

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    or other wood. The frame should be big enough for the largest prints to be
    made. Average inside frame dimensions would be 38.1cm x 50.8cm (18" x 24").
    Make sure that the corners are square and the frame lies flat against a flat
    baseboard or table top. The baseboard can also be made of 1.9cm (3/4")
    plywood. A few coats of shellac on the wooden frame will make it longer
    lasting and less apt to warp.
 
2.  Stretch the silk very tightly over the underside of the frame, using tacks
    every 2.5cm (1"). Make sure that the threads of the silk run parallel with
    the edges of the frame, pull the silk over the outside bottom edges and tack
    the silk around the outside of the frame (see Figure 2).

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3.  Make a squeegee (see Figure 3).

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PRINTING
 
1.  Cut the stencil and attach it to the screen (see "Preparing a Paper Stencil").
 
2.  Place the paper or cardboard to be printed under the screen and stencil.
    Draw about 10ml (2 teaspoons) of water-soluble paint (for example, finger
    paint) in a line along the edge of the silk just inside one end of the frame.
    The paint should be thick, about like auto transmission grease, so that it
    will not just fall through the screen without being pushed by the squeegee.
 
3.  Using an edge of the squeegee, pull the paint across the surface of the silk.
    This squeezes the paint through all the open areas of the paper stencil. Lift
    the screen and remove the print, replacing it with the next piece to be
    printed. Pull the paint back in the opposite direction for this print. The
    correct technique is to put an amount of paint on the screen that will,
    combined with the right pressure on the squeegee, produce a good print with
    one stroke of the squeegee. <see figure 4>

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    Make sure that the paint
    contains no dried paint
    particles. They could damage
    the screen.
 
4.  When a printing is completed,
    pull the stencil off the screen.
    Remove the wing nuts and
    wash the frame under running
    water.
 
5.  The pieces to be printed can be registered (lined up so that the printed
    image appears in exactly the same place on each piece). Registration guides
    can be made of thin cardboard or several layers of tape (see Figure 2).

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    Thicker guides could break the silk when the squeegee presses the screen
    against them. The guides should be taped on the baseboard at the edges of
    three sides of the sheets to be printed.
 
6.  If more than one color is to be printed, registration becomes very important.
    The procedure to follow is this:
 
    o   Print the first color, using registration guides.
 
    o   Wash the screen as in Step 4 above, and attach the next stencil.
 
    o   Place a piece of waxed paper or thin translucent paper under the
       second screen to be printed, and tape this paper on one edge.
 
    o   Print an image of the second screen on this paper.
 
    o   Raise the screen.
 
    o   Slide a sample of the first printing into position beneath the taped
       paper. Adjust the sample so that the second image will appear in the
       right place on the pieces already printed.
 
    o   When the sample is lined up, carefully hold the first printing sample in
       position and remove the wax paper.
 
    o   Tape new registration guides on three sides of the sample.
 
    o   More colors can be printed by returning to Step 6.
 
7.  Several colors can be printed over one another if transparent paints are
    used.
 
8.  A drying rack (see Figure 5) is helpful when many prints are to be dried.

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Source:
 
John Tomlinson, VITA Volunteer, Rochester, New York
 
PREPARING A PAPER STENCIL
 
This method of preparing a stencil for silk screen printing is more versatile for
some effects than the usual stencil technique: for example, the letter "O" can be
formed without connecting lines to hold the center in place. But the method has
these limitations: Images must be bold and simple designs. The stencil will last for
only a few hundred impressions; will not hold up with water-base paint; and
cannot be stored.
 
                             Tools and Materials
 
Stencil paper--Somewhat-transparent white bond paper works well. Commercial
stencil paper can be used, but the edge of the printing may be fuzzy. Thick paper
leaves a thick layer of paint when the squeegee draws the paint across the
screen.
Mimeograph stencils can be used to reproduce typing.
Stencil knife
A small-blade knife with a handle about as thick as a pencil.
 
To prepare and use the paper stencil, follow these steps:
 
o  Place the stencil paper over the image to be reproduced and fasten both to
   a hard level surface, like the baseboard of the silk screen.
 
o  Trace the design and then cut around the areas where one color is to be
   printed. Press just hard enough to cut through the stencil paper without
   cutting the original. Do not strip the cut-out parts away yet; leave the
   stencil intact.
 
o  Put a pad of newspaper on the baseboard of the silk screen so that when
   the screen is lowered it will hit the stencil firmly.
 
o  Place the stencil on this pad in the position desired. Slip several pieces of
   tape, sticky side up, under the edges of the stencil; this will tape the stencil
   to the screen when the screen is lowered. Mask the open areas of the
   screen beyond the edges of the stencil.
 
o  To make the stencil stick to the screen, draw paint across the screen with
   the squeegee.
 
o  Remove the cut-out parts of the stencil.
 
o  At the end of the printing run, peel the paper stencil and masking from the
   screen. Clean the screen.
 
A mimeograph stencil is prepared as it would be for a mimeograph machine.
Attach it to the screen the same way a paper stencil is attached.
 
Source:
 
Mrs. Benjamin P. Coe, VITA Volunteer, Schenectady, New York
 
MAKING SILK SCREEN PAINT
 
The paints described here for silk screen printing should have a shelf life of
several months when they are stored in jars with tight-fitting lids. The recipes
have been tried successfully in a temperate climate. Paints colored with powdered
tempera are more brilliant than those colored with food colors or ink. Other
water-soluble dyes can probably be used also.
 
                                   Materials
 
Starch or cornstarch
Soap Flakes
Gelatin (optional)
Coloring matter (food color, tempera powder, ink, or a dye of some sort that is
water soluble)
 
Recipe #1
 
Linit starch (not instant) 115 ml (1/2 cup)
Boiling water 345ml (1 1/2 cup)
Soap flakes 115ml (1/2 cup)
 
Mix starch with enough cold water to make a smooth paste. Add boiling water
and cool until glossy. Stir in soap flakes while mixture is warm. When cool, add
coloring.
 
Recipe #2
 
Cornstarch 57.5ml (1/4 cup)
Water 460ml (2 cups)
Soap flakes 29ml (1/8 cup)
 
Bring water to a boil. Mix cornstarch with a small amount of cold water and stir
the two together. Bring, to a boil and stir until thickened. Add soap flakes while
warm. Color.
 
This recipe produces paint that seems quite lumpy but this does not affect the
printing quality.
 
Recipe #3
 
Dissolve 115ml (1/2 cup) cornstarch in 172.5ml (3/4 cup) cold water
 
Dissolve 1 envelope gelatin (15ml or 1 tablespoon, unflavored) in 57.5ml (1/4 cup)
cold water
 
Heat 460ml (2 cups) of water, pour in cornstarch. Add dissolved gelatin. Boil, and
stir until thickened. Cool and add 115ml (1/2 cup) soap flakes. Color.
 
NOTE: Adding 5 to 10ml (1 to 2 teaspoons) of glycerine to any of these
recipes will make the paint easier to use.
 
Never let dried particles of paint get mixed into the paint or fall onto the screen
because they may puncture the silk during the printing. A small hole in the silk
can be repaired with a small drop of shellac.
 
Source:
 
Mrs. Benjamin P. Coe, VITA Volunteer, Schenectady, New York
                         Inexpensive Rubber Cement
 
Inexpensive rubber cement can be made easily with ordinary gasoline and raw
sheet rubber.
 
Imported pastes are often expensive. Many of these are not good for mounting
pictures and similar materials; they soak through the paper and wrinkle both the
picture and the mount.
 
Rubber cement does not wrinkle the pieces to be joined. It has another advantage:
if it smears, it can be rubbed off with the fingers when it is dry.
 
     Tools and Materials
 
Ordinary gasoline: 250cc (16 ounces)
Raw sheet rubber in one piece:
  5gm (115 ounce)
Jar with lid
Stirring rod
Brown bottle
(*)Tin can
(*)Charcoal
(*)Small pieces of cloth
 
_________________
 
(*)Needed only if gasoline is colored.
 
                          * * * CAUTION * * *
 
    Gasoline will burn and explode, and the vapors can be a
    health hazard. Be careful when mixing or applying the
    cement. Do not inhale the gasoline vapors. Make the rubber
    cement in a well-ventilated place.
 
The rubber to be used should be a translucent, light-brown sheet. Any brand of
gasoline can be used. Some gasolines are highly colored. This coloring should be
removed so that the rubber cement will not stain when it is used. To remove the
coloring, pour the gasoline over common charcoal several times (see Figure 2).
 
Use a clean tin can with a hole in
the bottom. Put a small piece of
cloth in the bottom of the can to
keep the charcoal from falling into
the filtered gasoline. You may have
to change the charcoal several
times before the gasoline is clear.
 
Put the 5 grams (1/5 ounce) of raw
sheet rubber in a jar and pour in
the 250cc (16 ounces) of ordinary
gasoline (see Figure 1). Cover the
jar.
 
It takes about three days for the rubber to dissolve completely in the gasoline.
Stir the mixture several times during this period, especially when the mixture
becomes thick. If some of the rubber does not dissolve, more stirring will break it
up. When the rubber is dissolved, you will have a smooth, milky-colored cement.
 
To store the rubber cement, it is best to use a brown bottle because the cement
will become thin if it is exposed to sunlight for a long time.
 
Mark the bottle:
 
                         DANGER: EXTREMELY FLAMMABLE,
                         HARMFUL OR FATAL IF SWALLOWED
 
The cement should be kept in a ventilated cupboard when it is not being used.
 
To make a handy dispenser for the
cement: Cut a hole in the cover of
the jar, large enough for the
handle of a 2.5cm (1") brush (see
Figure 3). Push the handle through
the hole and leave the brush in the
jar. This should be airtight because
the cement hardens quickly when
exposed to air.
 
Source:
 
Bunyard, Robert J. "Rubber Cement in a Tropical Climate," The Multiplier, Vol. 2,
No. 6, July 1956.