A Rudimentary Guide
to the Little-Known Art of
Photo-silkscreen
(C) 1977 Todd Walker and Becky Gaver
Building the Screen
The screen frame should be sturdy, light, well-nailed and glued. One of the simplest ways to build such a frame is with 1 x 2 cedar or pine from the lumber yard. The corner joints may be made solid in this manner:
The fabric recommended for this gelatin photoprocess is monofilament 200 mesh. Silk is not compatible with this method and is more expensive. Nylon is not dimensionally stable and makes registration of succesive images very difficult.
The fabric is stapled along the underside of the frame, stretched as tightly as possible without tearing. After stapling in place, the fabric should be washed thoroughly using a kitchen sponge and a kitchen cleanser such as Ajax, and rinsed to remove any residue.
To retain the ink during printing, there should be a safe edge around the screen appoximately an inch wide. It is applied with a 1" piece of matte board used as a squeegee, dried, and recoated with a brush. either acrylic medium or printer's padding compound is sensitized to light with a level 1/4 teaspoon of ammonimum dichromate cyrstals added to each ounce of either material, and thoroughly mixed. When applied as described, and dry, this should be exposed to sunlight for an hour or longer to ensure its permanence. The wood frame itself may also be protected with the same substance, which is impervious to most solvents.
Light-Sensitive Coating for Fabric
WARNING: AMMONIUM DICHROMATE IS POISONOUS AND, AMONG OTHER THINGS, IS KNOWN TO BE A HUMAN CARCINOGEN. IT SHOULD BE HANDLED WITH EXTREME CARE !!!One small envelope Knox (or other brand) gelatin, containing 1 teaspoon (7 grams) of gelatin, is added slowly with stirring to 2 1/2 ounces (65 ml.) of cold water. Allow to stand for 15 - 20 minutes, then warm to 120 - 130 degrees by placing the container in hot water until the solution is warm and very fluid. To this warmed gelatin solution, add 1/4 level teaspoon of ammonium dichromate crystals, mix thoroughly, pour into coater, and coat screen fabric. This amount is sufficient for two or three screens. (Note: Once the ammonium dichromate has been added, the coating, exposure, and washout of the exposed screen must occur within two hours - less under humid conditions - or the image may not wash out satisfactorily.) Adding the dichromate makes the gelatin light-sensistive, and all steps through washout should be done under subdued light. A yellow "bug" light is an excellent safelight for the process.
A coater, for the application of the sensitized gelatin, may be made from right-angle aluminum stripping available from most hardware stores. A section of this is cut to the width of the screen to be coated, the ends are closed, and a support handle or handles are added for convenience. Surfaces should be joined with epoxy glue, and should first be scratched or sanded for proper adherence.
The cleaned screen is placed in a steady position, with the area under it protected with newspaper. The warm gelatin is poured into the coater (previously warmed with hot water as well). Holding the coater level so the gelatin does not spill out, coat the screen slowly and smoothly. It is best to do this in one even pass if possible. The coating is quickly dried with a fan or with mild heat and then coated a second time from the opposite direction to eliminate all pinholes. When throughly dry, the screen is ready to expose.
Most failures can be traced to: (1) inadequate cleaning, (2) gelatin which has begun to spoil (once a liquid, it will not keep for long without refrigeration or addition of a preservative), or (3), too much or too little ammonium dichromate.
Exposure
Exposure is made through a positive help in intimate contact with the bottom (flat) side of the screen. Using a 500 watt, 3200 degree bare bulb at 24", the exposure would be, with a properly processed Kodalith or equivalent positive *, approximately 12 - 15 minutes. With other light sources, the exposure should be about 10% longer than that required to eliminate pinholes in the open areas. The minimum exposure will give the most precise rendering of fine details in the image. After proper exposure, the image will appear on the screen as a faint brownish negative.
* A positive is commonly a photographic image on film, but other methods work as well: acetate, glass, or any other clear, transparent material can be the support, with the image drawn, painted, cut out of paper, etc. The only requirement is that the image be completely opaque (no light shows through it when placed in front of a bright light), or detail will be lost when the screen is exposed. Suggested opaque materials are: India ink, photographer's red opaque, red or black paper, or "rubylith" (thin, translucent, adhesive-backed red blocking film cut like a stencil).
To wash out the exposed screen, the screen is first wet all over with cold water, then sponged gently with water at 110 degrees - 120 degrees on both sides until open and clean. The screen should be blotted on both sides with newspapers, then dried with a fan. Excessive heat should not be used for drying at this stage, or the image may be damaged.
After drying thoroughly, the image is examined and any pinholes or other flaws may be corrected with unsensitized gelatin, or LePage's glue, or other water-soluble blockout materials. The image on the screen is now ready for printing.
Printing
The screen is fastened to a large table or other secure surface with ordinary hinges and wood screws. There will be two holes in the end of any screen attached in this way, which are used whenever the screen is to be printed again. There are special screen clamps (available from the larger screenprinting suppliers) which are bolted to the table, into which a screen is tightened with wing-nuts. This is a faster, more efficent way of attaching and removing the screen.
A kick-bar (a length of 1" x 2" with a large hole drilled in it, and a screw loosely passed through it, allowing the bar to swing freely) is attached to the side of the screen frame. It acts as a support to keep the screen elevated above the printing surface when necessary.
To provide a rest for the squeegee when it is not in use, a large screw is driven part way into the far end of the screen frame.
On the near end of the screen frame, the top half of a double-hung window latch is attached. The bottom half is permanently screwed to the table. This arrangement permits the screen to be securely latched to the table during printing to assure close contact of screen and paper.
All paper should be cut to a uniform size for accurate registration of sucessive colors. The paper is held in place with three file signals (small clips available at office supply stores) which are taped to a cardboard backing. These clips remain stationary unless the size of the printing paper is changed, in which case the clips may be moved closer together or farther apart, as needed.
Any standard screenprinting ink may be used. For printing on paper, to be more certain that the image is in permanent colors and that the successive ink layers will adhere to each other, the following materials are recommended:
| Nazdar: Transparent base 5530 White 5535 Halftone base 6500 Binder varnish 5549 |
Advance: Transparent base JRP 800 White JRP 120 Halftone base PRO 850 Binding Clearflex JRP 880 |
These bases are mixed as follows:
|
For transparent color: 1 part transparent base 1 part halftone base 1/5 part binder varnish or binding clearflex Artist's oil colors are then added to desired color |
For opaque color: 1 part transparent base 1 part white 1 part halftone base 1/3 part binder varnish or binding clearflex Oil color as desired. |
To mix the ink, combine the desired bases and pigment in a bowl and beat well with a spatula. To properly disperse the oil color in the base, it helps to mix a palette-knife-full of the base mixture with the oils on a scrap of cardboard first, rather than squeezing the paint straight into the bowl. When the ink is the proper consistency, it will flow in a thin ribbon or band from the spatula held a few inches above the bowl. Turpentine may be added to thin the mixture. Ink which is too stiff or too runny will not pass through the screen properly.
Once the screen and image are alighed and secured, and the ink is ready, printing can begin. The screen is latched in place against the paper, and a generous line of ink is spread across the top of the image, beyond the image. The squeegee is held approximately 35 degrees - 45 degrees off vertical (for a sharp edge to push the ink through the fabric) and is pulled in one methodical sweep with hard, even pressure to the bottom of the screen. Then the squeegee is tilted to scoop the excess ink back to the top again, and is rested against the screw. The screen is unlatched and carefully lifted, the print is removed (checking for flaws), a new sheet of paper is put in place, and printing proceeds.
Dry prints on a rack, or hung back-to-back on clothespins strung on a line. Drying time varies from two hours to two days, depending on the humidity, etc. Later layers take longer to dry because of the ink buildup.
Cleaning the Screen
After printing, the surface under the screen is padded with newspapers, and excess ink is scooped out of the screen with cardboard scraps. Then the ink residue is cleaned with paint thinner, turpentine, or solvent for the screen ink used. While the solvent is still damp, use Ajax and cold water with a sponge to emulsify and remove the remaining ink residue. Rinse throughly.To remove the gelatin image from the screen, apply chorine bleach (Clorox, Purex) with a cheap nylon brush and gloves. Rinse well. Examine for stubborn areas and repeat if necessary. Finally, wash with cleanser and rinse to remove traces of cleanser. Dry with fan. Screen is now ready for a new image. The above cleaning methods will destroy silk, but will not harm nylon or polyester.
(Todd Walker handed out copies of this publication to students in his Non-Silver Photography class, ART 444, at the University of Arizona, fall semester, 1984.)
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This page was created by a friend and student of Todd Walker's. Thanks to Melanie Walker, Todd's daughter, for her encouragement in this endeavor! If you have comments, please email Jerry Ferrin.
This page was last updated March 24, Y2K.