Wednesday, 26 October 2011

WIDFP? - Screen Printing

What is screen printing?
A printmaking technique that uses a woven mesh to support an ink blocking stencil.

Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms an open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A roller or squeegee is moved across the screen stencil, forcing or pumping ink past the threads of the woven mesh in the open areas. (link)

What is the 'screen'?
Screen printing is also a stencil method of print making in which a design is imposed on a screen of silk or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced through the mesh onto the printing surface. It is also known as silkscreen, serigraphy, and serigraph printing. (link)

The screen is made of a porous, finely woven fabric (silk was used originally, but now polyester or nylon is used primarily) stretched on a frame constructed of wood or aluminium. A stencil is created from a non-permeable material to block out the negative areas of the image. The area where the ink will flow through will be kept open. (link)

There are several ways to create a stencil for screen printing. The simplest is to create it by hand in the desired shape, either by cutting a piece of paper or plastic film and attaching it to the screen (between the screen and the printing surface). (link)

Screen printing terms?
There are various terms used for what is essentially the same technique. Traditionally the process was called screen printing or silkscreen printing because silk was used in the process. Currently, synthetic threads are commonly used in the screen printing process. The most popular mesh in general use is made of polyester. There are special-use mesh materials of nylon and stainless steel available to the screen printer. (link)

When was it invented?
Screen printing was first patented in England by Samuel Simon in 1907. It was originally used as a popular method to print expensive wall paper, printed on linen, silk, and other fine fabrics. (link)

How does it work?
The equivalent of the printing plate for the screen printer is the screen - a wooden or aluminium frame with a fine nylon mesh stretched over it. The mesh is coated with a light sensitive emulsion or film, which -when dry- will block the holes in the mesh. The image that needs to be printed is output to film either by camera or image-setter. This film positive and the mesh on the screen are sandwiched together and exposed to ultra-violet light in a device called a print-down frame. The screen is then washed with a jet of water which washes away all the light sensitive emulsion that has not been hardened by the ultra-violet light. This leaves you with an open stencil which corresponds exactly to the image that was supplied on the film. Now the screen is fitted on the press and is hinged so it can be raised and lowered. The substrate to be printed is places in position under the screen and ink is placed on the top side of the screen, (the frame acts also as a wall to contain the ink). A rubber blade gripped in a wooden or metal handle called a squeegee (not unlike a giant wind-screen wiper) is pulled across the top of the screen; it pushes the ink through the mesh onto the surface of the substrate you are printing. To repeat the process the squeegee floods the screen again with a return stroke before printing the next impression. (link)

The screen is placed on a piece of fabric, such as a t-shirt, apron or bag. The ink is placed above the image on the screen and is spread across the screen using a rubber bladed squeegee. The squeegee forces the ink through the mesh of the screen and onto the chosen surface. Once the screen is lifted, you will see the newly created image beneath it. The screen can be used again and again. If used quickly you can do several prints in a row with out the ink drying in the screen. You can use the same screen with a different colour after washing and drying the screen. If you want to print with multiple colours with multiple screens, you will need to let the first application of ink dry then apply the next, working from lightest to darkest colours of ink. (link)

Screen printing on paper?
Papers that work well for this technique are drawing paper, construction and cover stock. Avoid using papers that have a high gloss or coating. For fine art quality prints 100lb weight papers or higher work well. Water-soluble and acrylic inks work well on these papers. (link)

Screen printing on fabric?
Most fabrics work well except nylon types. It is always a good idea to do a test run before getting involved in any project. Be sure to pre-wash your fabric to remove any dirt and sizing. This will ensure that the paint will adhere properly. Textile paints are used, they are later heat set when the project is completed and dry. Be sure to wash your screen quickly after you have finished your last project. Otherwise the paints will dry. (link)

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