Screen Printing

“Silkscreen is based on the principle of the stencil… in silkscreen printmaking, stencils, or shapes made with material thick enough to fill in (open areas) block the ink. The ink moves through the screen in the unblocked areas and prints onto paper or another surface placed below the screen… The modern silkscreen process is a straightforward and simple way to accomplish multicolor printmaking…. Unlike other printmaking methods, the silkscreen image is not reversed when printed but appears in the same direction as the original.”
From Basic PRINTMAKING Techniques by Bernard Toale

Screen Prints, Serigraphs, Silkscreen Prints
Silkscreen printing is basically a stenciling process. Simply stated, in screen printing, ink is transferred to the paper by being squeezed through a fine mesh (the screen), whereby the image is created by the use of stencils through which the ink does not pass. The screen consists of mesh stretched on a frame. A squeegee is used to force the ink through the exposed sections of screen.

Notes on Mesh
• The lower the mesh count the larger the open areas.
Larger open areas allow for more ink flow.
Use a lower mesh count for less delicate deigns.
• The higher the mesh count the finer the open areas between the crossing fibers.
Very fine mesh is needed for halftone
Monofilament Polyester (Yellow)
•195-230 Best for handmade stencils or painterly strokes
•230-305 For fine detail
•240-260 best for water-based ink
•260-305 is best for fine photo or computer generated imagery
Multifilament Polyester (White)
•Strength of fiber is denoted by x’s.
X= weakest
Xxx= strongest
•Average 12xx-14xx
•Textile 8xx-10xx

Tape
•Water-resistant tape on the frame prevents ink from leaking under the frame lumber and keeps the edges of your prints clean.

Frame size
•The screen should be approximately 3” larger in width from the inside and 6” in length than the printing area. Ex. An image which is 18”x 24” should be on a 21”x 30” frame.

Squeegees
•The squeegee should be 2” longer than the width of the printing area.
Types of squeegees:
•Rubber- generally gray or tan
*Polyurethane- generally clear or amber, sometimes green (recommended)
•Squeegee blades are shaped according to projects, do research if you plan doing something special otherwise a squared blade is good for general printing.

Scoop Coater
•The scoop coater is used to coat screen with screen filler after the drawing fluid has dried or to coat the screen with photo emulsion.

Inks
•Permanent Acrylic Ink – water-based ink that dries water-resistant. This type of ink must be washed out of screen immediately upon finishing printing or it will permanently adhere to the screen and ruin the mesh.

Additives
Extender Base- may be mixed with the acrylic ink to extend the pigment. A little will give you more ink to use without affecting the opacity too much, however if you use more than 50% base the ink becomes noticeably more translucent.

GOLDEN Silkscreen Medium- is a water-borne system designed to blend with acrylic paints for silk-screen application onto paper, wood and other suitable fine art materials. This product is designed to increase working time and prevent paint from drying in the screen too quickly.

GOLDEN Retarder- increases your “open” or work time by slowing the drying time.

Printing Tips
•Make sure there is a generous amount of ink on your screen.
•Flooding in one stroke evens out your Ink.
•The squeegee should be at a 45 degree angle.
•Print with an ample amount of pressure on your squeegee Keep your pressure even.

Making Multiple Color Separations

When printing multiple colors you need to think of each color as a separate layer and design accordingly.

• Create your image keeping in mind which color will go where. Remember that the results of silkscreen printing are often flat even colors so design your image accordingly.
• Identify the darkest color (often black) in the design.
• Use tracing paper, paper and a light table, or the computer to separate only the darkest color in your the design. This will be your "key" printer - the guide that all the other colors are keyed to. Black is often used to "trap" other colors - that is, outline them - and since it will be the last color printed, it will overlap anything it traps.
• Make a separation for each of the other colors in your design (for example, if yellow and red are your other two colors, you'll have three tracings: one for black, one for yellow and one for red). Place each of these separations over the black and make sure they match up (register) reasonably well. This is a color separation.
• Transfer each separation onto different silk screens, an isolated area on the same silk screen or do the process one by one. Do this by laying the separation on the screen and flipping the screen over so that you can see the tracing through the screen; trace the design onto the silk screen with a soft, dull pencil; then render, using drawing fluid and screen filler, screen filler, or photo emulsion. Each color will have its own stencil.

Tips
• These colors will be recombined later in the printing process. Keep your design simple for ease of printing and registration.
• The highlights of your design will be the white of your paper or fabric. In creating your design, don't overlook the opportunity to use these highlights to your advantage.

Stencil Techniques

SCREEN FILLER METHOD
Direct Block-out or "Negative Method"; drawn/painted areas do not print

The Screen Filler is used to block out areas that you do not wish to print. This allows the ink to be forced through the screen wherever the Screen Filler has not been applied.
Since Screen Filler is applied to all areas that are not to be printed, this is considered to be a "negative" method of printing. Your print will be the opposite of that which you created on your screen.
• Trace the first color of your design onto the screen with a soft pencil.
• Stir the Screen Filler until it is thoroughly mixed to a smooth consistency. Select an appropriate brush. This will be determined according to the type of line or texture to be produced. You can work on either the front or back of the screen. Be certain that the bottom of screen is elevated-not touching the table. Paint areas of the layout that you do not want to print. When all areas to be blocked out are covered with Screen Filler, flip the screen over and smooth out places the filler may have collected on the opposite side of the screen. Be careful during this smoothing out not to distort your work.
• Leave the screen to dry in a level position. Make sure nothing touches the areas covered with Screen Filler. Thorough drying is necessary. Overnight drying is recommended to assure best results.
• Check for pinholes in the blocked-out areas. You can do this by holding the screen up to a light. Fill any pinholes with screen filler and allow to dry completely. You are now ready to print.
• Trace the second color of your design onto the screen and repeat the steps.

DRAWING FLUID - SCREEN FILLER METHOD
Tusche-resist or " Positive Method”;drawn/painted areas print the ink color

Any area where you put drawing fluid will print as a positive - that is, ink will come through the open mesh during the printing process.
• Trace the first color of your design onto the screen or you may choose to paint freehanded with the fluid onto your screen.
• Select an appropriate brush. This will be determined by the type of line or texture to be produced. You can work on either side of the screen.
• Be certain that screen is elevated-not touching table. Paint the Drawing Fluid over those areas of your separation that you want to print. Leave the screen to dry in a level, flat position. Make sure nothing touches the areas covered with Drawing Fluid.
• After the Drawing Fluid is completely dry, open the Screen Filler and mix it thoroughly to a smooth consistency. Spoon it onto the screen fabric on the same side of the screen used for the application of Drawing Fluid.
• Use the squeegee or the plastic spreader to apply an evenly smooth coating of screen filler over the entire screen. One pass should be sufficient. Multiple passes of Screen Filler will dissolve the Drawing Fluid and prevent character washout.
• Place the screen to dry in a horizontal position making sure nothing touches the fabric. It is important that the Screen Filler dry completely.
• When the Screen Filler has thoroughly dried, spray cold water on both sides of the screen. DO NOT USE HOT WATER DURING THIS STAGE. Concentrate the spray on the areas where Drawing Fluid was applied. These areas will dissolve and the screen will become open at those points so that ink can flow through them.
• If some areas remain slightly blocked, scrub them lightly with a small stiff brush on both sides of the screen (an old toothbrush will do a good job). Allow your screen to dry in a level (horizontal) position, bottom-side up.
*Drying time may be accelerated by using a hair dryer or fan.
• After you rinse out the drawing fluid and let the screen dry, you can touch up or refine your drawing with screen filler.

Technical Notes:
1. Always wash acrylic ink out of screen immediately after you are finished printing.

2. Always tape the edges of the screen so that ink cannot get under the frame.

3. Drawing fluid must be dry before applying screen filler.

4. Screen filler must be dry before washing out areas where drawing fluid was used.

5. DO NOT use hot water when washing drawing fluid out of the screen. The hot water may also wash out the screen filler.

6. When you are finished with the image, rinse ink out of screen, then rinse drawing fluid and screen filler out. To clean screen filler, wash the screen with dish detergent (or Grease Lightning if necessary), water and a sponge, then let it sit wet for a few minutes and hose it down with the power washer. When you are finished, give it one last wipe with degreasing liquid, rinse that out and store your screen or place it in front of a fan if you’d like it to dry more quickly.

PHOTOGRAPHIC EMULSION METHOD

This is one of the most exciting methods of Screen Printing because it offers the widest range of possibilities. It makes possible the printing of fine line drawings, various hand and commercial lettering techniques, as well as photographic halftone positives.

All methods of photographic Screen Printing require three things:
• a screen prepared with a light-sensitive coating
• a film positive, or equal
• a light source that will enable you to transfer the opaque
images on your positive to the light sensitive screen you
have prepared.

• Step A--Mixing the photo emulsion
SPEEBALL DIAZO SYSTEM:
SB4558 Diazo Kit Follow the mixing instructions given on both containers. Store the sensitized emulsion in a cool and dark place. Shelf life for the sensitized emulsion is 4 weeks at 90 Degrees F, 8 weeks at 70 Degrees F and 4 months when refrigerated.

•Step B--Coating the screen
Coat the screen by first pouring the emulsion into the scoop coater. Rock the scoop coater back and forth slightly to move the emulsion towards the edge. Pull the scoop coater with emulsion upwards against the screen stopping at the top and catching any excess emulsion. Cover the entire screen. Work to achieve a continuous, even THIN coating on one side of the screen fabric. Many choose to coat both sides of the screen. At home if you do not have a scoop coater you can use a squeegee to spread the emulsion. Return any excess solution to your emulsion container.

•Step C--Drying the coated screen
In an area AWAY FROM LIGHT AND HEAT, set the screen against the wall to dry. Do not allow the wet emulsion to touch anything. Allow the screen to dry thoroughly. Once the sensitized screen is dry, it must remain in a darkened area until it is ready to be exposed. A fan in the dark area will greatly speed up the drying of the emulsion on the screen.
With the SPEEDBALL Bichromate System, the maximum allowable time between application of the sensitized emulsion to the screen and the exposure is 6 hours at room temperature. With the SPEEDBALL Diazo System, the maximum allowable time is eight weeks at room temperature.

• Step D--Preparing a positive
A "positive" is any opaque image (usually black), on any transparent or translucent surface. There are many ways you may choose to prepare them. The graphics must be opaque.
One way of producing positives is through copy machines that have the capability of reproducing very opaquely on film, vellum, tracing paper, etc. In order to satisfactorily produce a positive using a copy machine, the following conditions must be met:
. (1) Black and white line work-Must be opaque
. (2) Photographic print-Must have high contrast
. (3) Copy machine must have capability stated above. You must check this out in advance.
Another way of producing positives is through the computer. Scan your image into the computer and use a program such as Photoshop to separate colors. Your separations should be made into black and white images. To reproduce photographs you may wish to use the halftone filter in Photoshop. Some printers may offer halftone as a printing option.

A third option is to make a laser print or photocopy following the above guidelines on white laser or copy paper. After the image has been printed on the paper saturate the back of the paper (non-image side down) with vegetable oil. Exposure time may be slightly longer.

Photographic images can also be accurately screen-printed. However, because of the halftones (or continuous tones), which are in all photographs, a special type of "positive" must be prepared. This must be done by someone with photographic expertise and who has the necessary equipment. Essentially, this person will photographically transfer the halftones to Kodalith Ortho film. A dot patterned half-tone screen will be placed between the lens, and the ortho film. These "halftone" dots will be exposed to the film simultaneously with the photograph. The resulting "halftone" negative will then be converted by the photographer to a "halftone" positive. This is the same type of "conversion" that is made in the preparation of photographs for newspaper and magazine printing. The dot pattern breaks up the continuous tones into a half-tone interpretation that can be printed.

Fine art half-tone screen-printing involves a posterization process whereby a series of selected positives are produced through a process camera. With filters, the process camera can selectively identify specific colors in the original art. These are then, sequentially prepared for color registry. This is a highly technical procedure and should be attempted only by experienced printers.

• Step E-- Exposing
Before you remove the sensitized screen from the dark drying area, make sure everything you need to print with is on hand. Set up your exposure unit (lamp if you do this at home) and positives which can be fixed in place with transparent tape. It is better not to overlap positives. Once your "positives" are in place and against the fabric, you are ready to expose the screen.

Home exposing
To set up your "Light Station" place the screen on top of a piece of black paper and center it 12 inches directly below a 150W clear incandescent bulb or a BBA No.1 Photoflood (preferred) Bulb. Either should be fitted with a foil-type pie tin as a reflector.
The positive can be placed in contact with the coated (dry) screen with a heavy sheet of glass placed on top for pressure. Another method employs the use of a foam rubber cushion, which is cut to the inside, dimensions of the screen frame. The positive is placed in reverse (mirror image) on top of the underside of the screen.

SPEEDBALL SCREEN PRINTING SYSTEM
Recommended Exposure Chart
150 Watt Bulb, Clear Incandescent
Screen Size 150W Bulb Height Exposure Time
8" x10" 12 inches 45 minutes
10"x14” 12 inches 45 minutes
12"x18” 15 inches 1 hr. 14 minutes
16"x20” 17 inches 1 hr. 32 minutes
18"x20" 17 inches 1 hr. 32 minutes
BBA No. 1 Photoflood (250 Watt)
Screen Size Lamp Height Exposure Time
8" x 10” 12 inches 10 minutes
10"x14" 12 inches 10 minutes
12"x18" 15 inches 16 minutes
16"x2O" 17 inches 20 minutes
18"x2O" 17 inches 20 minutes
PLEASE NOTE: This chart has been prepared using an aluminum foil pie-plate reflector

More sophisticated light sources, reflectors and equipment can, of course, be used. However, as any variable is changed, you will have to adjust the exposure times and distances. This will require experimentation through the use of test strips or other light testing devices or procedures.

Turn on the light and note the time. Experiment with timing. If done at home expose according to time and distance indicated in chart. After exposure, remove positive and take screen to sink.

• Step F—Opening the image
Apply a forceful spray of water to both sides of the screen. DO NOT USE HOT WATER. Concentrate this spray on the light images. After a few minutes, these areas will become "open." Continue spraying until all unwanted emulsion is gone. Once you have completely washed the screen, let it dry thoroughly in a level flat position. Hold the dry frame to the light and check for pinholes. These can be covered with Speedball Screen Filler or pieces of masking/ block-out tape. If Screen Filler is used, let the screen dry again.

NOTE: Photo Emulsion should not be left in the screen indefinitely unless a permanent stencil is wanted. It should be washed out as soon as the run is completed.

Ruby Lith or Amber Lith

From the field of printmaking, ruby lith is thin, flexible, translucent, dark red material, used for masking areas of a light sensitive medium that shouldn't be exposed. It is slightly tacky on one side, and mostly stays in place on acetate or film or whatever. It comes in individual sheets stuck to a piece of acetate, or on a roll like tape. To use it, you usually use an x-acto knife to trace out whatever mask shape you want, then peel off the shape and put it wherever it's needed.

There are machines that use lasers to cut pieces of ruby lith very finely and in intricate shapes, but shops that can afford them have mostly gone digital nowadays. In fact, the use of ruby lith by any print shop is pretty archaic, since digital processing has become so cheap and common. This is too bad, as cutting and aligning a mask by hand is something of an art, or so I've been told.

Ruby Lith fun facts:

* Ruby lith is the reason that masks made in Photoshop are reddish, and referred to as rubies.
* The first microprocessors (and ICs in general) were designed using by cutting the conductor and transistor patterns in ruby lith, and then focusing them down in size with lenses to expose the doped silicon. This process is called photolithography.
* All of the artwork used in the OBEY GIANT project were designed by cutting ruby, even the lettering.

Registration

Multiple- Color printing
•Make sure you have separations made by drawing, tracing or computer printing
Each color in your print is a separate layer and therefore has its own stencil.
•Make sure your separations match up by layering them and viewing them on a light box.
•Transfer each separation one by one to your screen
Keep in mind color choice and layering. You may want to use your lightest separation first.

You will need:
•Sheet of Acetate or Mylar larger than your paper size
•Masking tape
•Proofing paper
•Editioning paper
•Screen and materials ready to print

•Cut your paper down to size (both proofing and editioning).
•Place screen in hinges and gather materials to print
•Tape the acetate to the table
The tape is a hinge for the Mylar.
•Make a print on the acetate
•Slide a piece of proofing paper under the acetate and position it correctly
•Raise the acetate and mark the position of your paper on the baseboard
•Print on the paper

Cardboard guides:
Optional; Figure out what works for you. This will give you something to butt your paper up against.
•Cut 1” x 2” cardboard or mat board strips
•Place them on your registration marks to use as a guide for your paper
•Tape them down to your baseboard or glue them with rubber cement

Common Screen Printing Problems

Most problems occur in the filling of the screen- the flood stroke.
Filling the screen properly before printing insures an evenly inked print.
The angle of the squeegee, pressure applied by the printer, and materials used all affect the print. Change in the printer’s movement, as well as the angle or pressure of the squeegee blade may show up as variations in the print. Be consistent in your printing! The printer’s goal is to learn to judge when a screen has been properly filled in order to pull a clean print.

Outcome
Areas are not printing, often along the sides
Problem
Uneven pressure was placed on the squeegee or the squeegee was not held at the proper angle
Outcome
Marks smudged or ink bled
Problem
Screen is over flooded- make only one pass when filling the screen using the proper amount of ink
Outcome
Detail is lost
Problem
Screen is over flooded or ink has clogged the mesh
Outcome
Streaks or patchy marks
Problem
Screen is improperly flooded- there may not be enough ink on your screen
Outcome
Print is unevenly saturated particularly in large open areas
Problem
Uneven flooding- there maybe more ink in areas and less in others
Outcome
Lines or marks on the print
Problem
Chips or protrusions in the squeegee blade