Introduction to Screen Printing
In this series on the screen printing process, we are going to cover the necessary steps required for you to print your own t-shirts. Step one is creating a film positive, which is the finished artwork needed to make a screen from which to print your shirts. A film positive is a sheet of clear plastic or paper vellum that has the artwork in black printed on it. (see illustration below). It’s very important that the black areas of your artwork be opaque (not allowing light to pass through.)
If your artwork has been created by hand you can send it out to a service company that can create a film positive by using a photographic process.Your best choice for generating artwork is with a vector based graphics program such as Corel Draw or Adobe’s Illustrator. This type art will give your lines the sharpest detail and make it easy to create your own film positive by printing your image out in black and white on to clear acetate or Mylar via a laser printer. These two options create the best line quality giving you a highly opaque image that will burn a crisp and clear screen image.
Another option, if your art work doesn’t have a lot of detail you can use a ink jet printer and output your image in black and white onto a special paper called drafting vellum. This type of paper allows light to penetrate through the white area of the paper and the light is blocked by the black ink area of the print which is what you want when you are making a screen using a photographic emulsion.
Types of Film Positives:
Photographic reproduction: Highest quality, totally opaque blacks, exact line reproduction at any size with minimal to no lose of resolution. Necessary for creating screen prints of fine detail, half tones and four color process printing. Down side is the high cost. Not economical for short production runs.
Laser printout to clear plastic vellum: Medium quality. opacity depends on the quality of printer. Also limited by the maximum size of the printers output. Reasonable cost per positive once the initial cost of buying a printer has been covered. This is the method used by most t-shirt printing shops.
Inkjet printout to drafting vellum or clear plastic designed for inkjet printing: Lowest quality but usable for artwork of low to medium detail. Two exact copies of your artwork can be doubled up and taped together with transparent tape to produce an image with higher opacity. Least expensive method but again limited by the output size of the printer.
Hand cut stencil using Rubylith: This is a two ply material. The base is a thick clear plastic adhered to a soft red semi-transparent ply. Although you can see through the red materal, it acts as if it were entirely opaque and blocks light.The Ruby is placed over your art work, dull side up, you’re able to see through it and the outline of the art is cut with the point of an exacto knife cutting only thru the soft red ply. Then the waste area of the image or what would be the white area is pulled away from the clear backing and disposed of. This material is typically used to create color separations.
The most basic of film positives: would be one in which you apply precut black letters to a sheet of clear plastic.
Three things to consider when creating art for screen printing are, size, colors and detail. The finished art work will need to be the exact size as the finished print. Each color in the print will require a different screen and therefore a different film positive. For our discussion here we are not going to go into great detail about multi-color printing but will be concentrating on the steps required to produce a one color t-shirt print. You must however be aware that for each color in a t-shirt print there is a separate screen.
If your image has a outline that will be printed in black or another dark color, any other colors in your image will be indexed to this outline and you will want them to overlap the outline slightly. This is called trapping and lets you create prints with no gaps between colors as well as making it easier to register you colors during the print process. To align the artwork for each screen color, artists use registration marks. These are cross hairs within a circle that are placed in each of the four corners of the art so that each new color separation can be placed on the original outline and lined up or registered to these marks. These registration marks become a critical part of the art and are actually burned into the screen along with the artwork. They are then used to align each screen on the printing press so that all colors fall into the right place.
Because screen printing involves pushing ink through cloth onto a unstable substrate, in our case a t-shirt, you are limited in the amount of detail you can use in your artwork. Especially if you are just starting and the type of equipment you are using is limited. There are some fantastic photographic reproductions done in t-shirt printing but this type of 4 color process printing requires highly sophisticated equipment and expertise.
Start out slow creating a one color t-shirt without a great deal of detail and gradually expand your equipment and knowledge to do multi-color work. Doing this you will find that t-shirt printing can be fun and profitable.
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