How to Use a 4-Color Printing Press
Offset lithography is the standard method used by commercial printers for color printing. Using a 4-color press, commercial printers produce high-quality, custom full-color printed materials. Top commercial printers can produce small business cards, large format posters, brochures, magazines and newsletters with eye-catching photographs and graphics in vivid color. Offset lithography has the advantage of producing good reproductions for an affordable cost on a wide range of papers. The process is fast and widely available. Offset lithography works because the oil-based ink adheres to the image area and is transferred to a blanket cylinder on the press, and then onto the paper.
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Things You'll Need
- Printing press
- Fountain solution
- Printing blanket
- Ink
- Paper
- Electronic densitometer
Instructions
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Obtain the text copy and the graphics from the person commissioning the print job. Make sure it is in the appropriate format. Ask that only the material to be printed be placed in the file to avoid misunderstandings. Make sure the materials are presented in a high-resolution format like a PDF or TIFF file format.
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Place the image information on a four thin metal plates. The image information includes text, illustrations, photographs, documents, and anything else that needs to be printed. Put the imaged plates on the cylinders of the 4-color press. Plates are held in place on the cylinder with a plate clamp. Each plate cylinder represents one of the four primary colors, cyan blue, magenta red, yellow and black. The water dampening cylinders will wet each of the four plates on the press.
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Check the density of the ink with an electronic densitometer. The electronic densitometer enables you to control the quality and consistency of the print run. The levels will have been set by the computer that sent over the images.
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Run a batch of paper through the press at low speed to check the alignment of the colors and to see if the ink flow is steady. Adjust the position of the plates if necessary. This process is called "make ready."
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Apply a coating if necessary to protect the printed piece and give it a shiny finish. Aqueous coating can be applied during the printing process.
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Tips & Warnings
Use a wetting agent or fountain solution to repel oil-based ink from areas on the plate that don't hold an image. Areas on the plate that have an image attract ink.
Separate the colors in the full-color image electronically and use the computer to send the images directly to the plate on the printing press. This process replaced the traditional process of producing negatives for each color.
Use a sheet-fed press to run individual sheets, and a web-offset press for very high volume printing.
For special effects, use such techniques as die cutting or embossing when the printed piece comes off the press. The printed material may also be scored, perforated, folded or bound.
References
Resources
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