The different types of screen printing stencils include photo stencils (also called emulsions), hand-cut stencils, and the tusche or block-out method.
Also known as silkscreen printing, screen printing is accomplished by forcing ink through a stencil attached to a piece of woven fabric stretched over a frame.
The essentials required for screen printing include screens, squeegees, screen printing inks, screen printing stencils, and screen or masking tape.
Screens are generally made up of two parts; the frame and the mesh that is stretched over it. The frame size and mesh count you choose will depend on the size of your project, the detail of your design, and the type of ink you use.
Squeegees are used for spreading ink on your screen. The size of the squeegee you use will depend upon the size of your screen.
Screen printing inks
Screen Printing Stencils come in three varieties, including emulsion, hand-cut, and block-out. For more information on stencils, see "What are the different types of screen printing stencils?" above.
Screen tape or masking tape is used to close off any openings on the screen. This prevents ink from seeping in around the frame.
Screen printing can be done on a variety of surfaces, including fabric, paper, glass, wood, metal, and plastic.
Cotton and cotton blends are the most popular fabric choice for screen printing projects because they absorb ink more readily than synthetic fabrics.
Silk absorbs ink very evenly, but is thinner than cotton. Silk fabrics absorb less ink, resulting in more subtle designs than those achievable with cotton or wool.
Polyester fabrics are less porous and permeable than natural fibers, so ink is less likely to adhere. If you wish to use polyester fabrics, look for inks specially made for use on synthetic materials.
Wool fabrics are highly absorbent, resulting in long-lasting, vibrant colors. Wool is best for simpler designs due to its texture and bulkiness.
Monofilament fabric is woven of a single thread. It is uniform in weave, giving a smoother ink flow that results in a sharper print. Multifilament fabric is woven of a twisted strand thread. It is less uniform in weave, but has more tooth for easier adhering of stencils and heavier ink deposit.
Monofilament fabric mesh count is determined by the number of threads per linear inch. The fewer threads per inch, the larger the size of the openings and the more space for ink to get through the fabric. Monofilament fabrics are designated by a number, such as 86 or 109.
Multifilament mesh size is determined by thread size. The number of threads per square inch stays the same. Multifilament fabric is indicated by a number followed by an XX — for example, 8XX or 10XX.
The following shows a rough equivalent between monofilament and multifilament fabrics:
Stencils can be created from paper, hand-cut film, and photographs.
The three main types of emulsions are diazo, SBQ-based or photopolymer, and dial cure.
Diazo emulsions are a good choice for novice screen printers because they are affordable and easy to use. They require the manual mixing of photosensitizer with resins. Diazo emulsions change color during exposure, letting you know visually the degree to which your stencil is exposed. However, diazo emulsions are less sensitive to light than other types of emulsions and require longer exposure times. The resulting stencil tends to be thicker, making diazo emulsions a poor choice for detailed prints or prints that require halftones. Once mixed, diazo emulsions will last a few months on the shelf.
SBQ-based or photopolymer emulsions expose within seconds, making them much faster than diazo emulsions. They are pre-sensitized, meaning that they are ready to use right out of the package with no mixing or other preparation required. The more delicate bonds created make them a good choice for detailed work. These emulsions tends to create a thinner stencil, but multiple coats can be layered if a thicker stencil is required. Pure photopolymer emulsions have long shelf lives, but most are not very water-resistant. As a result, they are not as well suited to waterbased inks.
Dual-cure emulsions combine diazo and photopolymer emulsions. Dual-cure emulsions are versatile and create very durable stencils. They require mixing and cure faster than diazo emulsions, but not as quickly as SBQ-based emulsions.
Cut a piece of film at least 1" larger than your artwork. Tape the film over your design on your work surface, with the film side up (not the glossy backing side). You can see through it to trace your artwork.
Using a craft knife, carefully cut along the edges of the design. Make sure not to cut through the backing sheet. Your artwork should be as simple as possible when you are just starting out — heavy line drawings, bold block lettering, free-form shapes, or geometrics that can be cut with a ruler work best.
Gently lift and peel away the shapes that you want to print. The film that is left will seal off the rest of the screen so that ink cannot pass through.
If you want to print with waterbased inks, use lacquer-based film which requires strong flammable solvent to make it adhere to the screen. Use caution and good ventilation. Once the screen is ready, you can print with any waterbased or solvent-based inks except lacquer, vinyl, or plastisol.
If you want to print with lacquer, vinyl, plastisol, or solvent-based ink, use watersoluble film. It adheres to the screen with cool water and washes out with warm water when the job is done.
Place the film right side up on a built-up surface, such as several layers of newspaper or cardboard, that is slightly smaller than the frame. Place the frame on top of the film. Weight the frame with ink cans or similar items so that the film makes good contact with the screen.
Using a lint-free cloth or sponge saturated with adhering solvent or water, blot the screen but do not rub. Get the film just wet enough to adhere. It will look darker where it has adhered properly.
Stand the frame up and use a fan to dry it. After 20 or 30 minutes, try peeling the backing sheet off. It will come off easily if ready. Use block-out and screen tape to seal off the rest of the screen and you're ready to print.
The advantage to photographic screen printing is that virtually anything you create in black and white (or black and clear) can be reproduced by this process. You must start with a film positive for each color you are printing in.
A film positive is required for use during the photographic screen process. It consists of an opaque image on a transparent sheet, such as acetate or prepared acetate, Mylar, or copier film. You can use vinyl stick-on letters, transfer lettering, India ink, or Rubylith masking film. You can also create a design on a computer and print it on a laser printer film.
A commercial printing company can convert your artwork to a film positive if you are unable to make your own. In order for any design to screen print well, your image must be sharp and high contrast. If your colors are going to overlap, you need a film positive and a screen for each color. If not, you can use one screen, block out areas with masking tape, and print your colors progressively.
There are two methods of photo screen printing.
With the direct method, the photo-sensitive film or liquid emulsion is applied to the screen, allowed to dry, and then exposed to the artwork (film positive) with the proper light source. There are direct liquid emulsions suitable for either solvent or waterbased inks, or both. Ulano CDF direct films are available for either type of ink.
With the indirect method, the photo-sensitive film is exposed to the artwork first, developed in developing solution or water, and then applied to the screen while it is still wet. The indirect method is only suitable for use with solvent-based inks.
All photo materials are sensitive to ultraviolet (UV) light. The black parts of your film positive protect those parts of the stencil that you want to print from being affected by the UV light.
After exposing your film or emulsion to the light, in contact with your film positive, these protected areas are washed out, leaving the hardened, non-image area of the stencil to seal the screen fabric and allow ink to pass through only the washed-out areas.
Sunlight costs nothing but is unpredictable.
Photoflood, 150 watt, or 250 watt bulbs are inexpensive, good for bold designs, and fairly dependable. Bulbs with higher wattage require shorter exposure time. However, bulbs may need to be changed often.
Blacklight is a moderately expensive yet very dependable method that delivers excellent results with fine detail and short exposure time.
Self-standing quartz halogen exposing units are very expensive but the best source for professional, continual use.
Similar to the hand-cut method, with the block-out method a brush is used to paint liquid block-out directly on your screen in the areas that you don't want to print, leaving open the areas where you want ink to pass through. In other words, the block-out replaces the film. Use lacquer-based block-out for waterbased inks and waterbased block-out for solvent-based inks. Be sure to properly prepare your screen by degreasing and abrading. Choose a screen mesh in a medium range — 140 or 12XX count.
Tusche is a black, waxy substance in liquid or solid crayon or pencil form that you use to paint or draw directly onto your prepared screen in a positive fashion. The areas you paint will be the areas that print. After the tusche is applied, coat the entire screen with a 50/50 mixture of hide glue and water or 50/50 gum arabic and water. Let that dry, rub out the tusche with turpentine, and you're ready to print. This method requires solvent-based inks.
The drawing fluid/screen filler method works like the tusche method, in that the drawing fluid acts as the tusche and the screen filler acts as the glue mixture. The benefit to this method is that the drawing fluid is washed out with cold water and the screen filler can be removed with hot water — turpentine is not needed. Any waterbased ink can be used. This is method is particularly suited for the classroom.