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Check out the rest of our library for working with SMR premium vellum

Instructions for screenmaking with Vellum
When should you use vellum?
Printing on Vellum
Determining Correct Exposure for Vellum
Vellum Tips & Tricks

How to Make a Screen Using Vellum

Most experienced screen printers will likely find this page of our vellum resource guide to be a bit too elementary, however, we have frequently fielded questions from individuals - particularly those considering entering the screen printing business - as to how screens are made. For the benefit of those individuals, or as an educational tool for your customers, here is an overview of the screen making process.

A screen starts as a frame and a piece of special fabric. Frames can be made of wood or metal. Historically, frames have been made of a number of other materials, even porcelain, but modern frames usually fall into one of these two categories. The frame in this picture is a special high-tech frame which provides it's own stretching mechanism. Fabric for screen printing is rarely made from silk these days, even though a few people still use the term "silk-screen." Most screen printing fabrics are made from precision crafted monofilament polyester, meaning that the strands of thread in the fabric are a single filament - like fishing line. These threads are manufactured to exacting standards where every thread is exactly the same diameter throughout the weave and the distance between threads in the weave is exactly controlled.
Fabric is attached to the frame and then stretched across the frame in both the  height and width dimensions. Stretching a frame forces the screen maker to walk something of a tightrope. Since the piece of fabric used on a single garment-size frame may cost more than $20, it is important that care is exercised not to tear the fabric when stretching. On the other hand, if the fabric is not extremely tight, the screen will produce poor-quality prints. A special device for measuring tension is a very wise investment to help you bring screens to optimal tension without costly breakage.

Modern screen fabrics can withstand tremendous tensions, and the fabric on a properly stretched 110 mesh frame feels much like placing your hand on a solid wall.

Once stretched, the screen undergoes an initial washing / preparation for it's first use. Special chemicals will be employed at this stage to degrease the screen and slightly abrade the smooth surface of it's fibers so that emulsion can firmly attach itself to the fabric.
After the screen dries, it is coated with a special photo-sensitive emulsion. The emulsion may be a liquid (direct) emulsion, or a film on a carrier sheet. (Indirect) Special techniques are employed in coating the screen so that no air bubbles form in the emulsion, and so that the emulsion coating is smooth and uniform.

The emulsion-coated screen is now light-sensitive, and must be placed in a special drying cabinet which allows air to pass over the screen to dry the emulsion, while keeping light out.

 
When the screen is dry, it is ready for a design is to be exposed or "burned" into it. To accomplish this, the design is printed onto a piece of SMR Premium Vellum, and the vellum is placed on the light-sensitized screen, with the design in contact with the emulsion. The exposure unit uses a vacuum or some sort of compression mechanism to ensure positive contact between the vellum and the screen to make sure that the design cannot move, and air space between the screen and vellum cannot create distortion. The exposure unit emits light with a high UV content toward the screen. Areas of the emulsion which receive this light harden, while areas where the printed design hold back light stay "soft."

See Also: Determining Correct Exposure for Vellum

Once the screen has been exposed, it is removed from the exposure unit and washed. "Soft" areas of the screen - the areas that did not receive light because light was blocked by the print on the vellum - wash away leaving the open mesh of the screen exposed. In the areas that received a proper amount of UV light, the molecules in the emulsion have "Linked" and hardened. These areas are very difficult to wash away, and form the stencil for the design you wish to print.
 
Once the screen has been dried, it is placed in a press for printing. Ink is passed over the screen, and the ink is pushed through the holes in the open mesh. But ink cannot flow through the areas where emulsion still coats the screen. When the screen is lifted from the garment, ink has formed a copy of the image that is on the screen. Once the ink has been cured or dried, the shirt is ready.