When printing a project one of the first things to consider is how you will have a document printed. This is important because it will affect decisions you need to make at the beginning of the design process in terms of setting up your documents. As we discussed in unit 3, color setup is very different for offset printing and digital printing. If you can think ahead you can save yourself trouble and extra work later down the line.
Digital printing is easily explained by thinking about your home inkjet printer. Most inkjets have 3-5 cartridges that convert your color during output. When you hit print on your computer the digital file is directly transferred to paper. Professional printers have digital presses that work like your home printer, but are calibrated to be much more exact in color output and print quality.
Digital printing is a great option when printing small jobs, usually less than 500 copies. Because the quantities are smaller the digital presses are often more efficient than an offset press because there is much less setup involved. They also allow for additional features to be added like variable text. Variable text takes a basic design and updates some portions of the copy on the fly for each person receiving the solicitation. If you were going to send a postcard you could personalize it with the name of each recipient. Because digital presses send design direction from a digital file to the final paper each copy can be unique in this way.
Offset printing is also called lithography. It works on the basic principle that water and ink don’t mix. Think oil and water–the two repel one another. Large printing plates are created with the image on it, moistened, and dipped in ink. The water adheres to the non-image areas and the ink adheres to the image areas. Once the plate has picked up the ink it is transferred to a rubber blanket which is then pressed on the paper. Because the engraved plate doesn’t make direct contact with the paper, but uses the intermediary rubber blanket to transfer the ink, the name offset printing was coined.
The illustration above shows how the paper is moved through the press. In the upper left you see that the water and ink are first picked up by the Plate Cylinder. The ink is then transferred to the rubber (blanket) cylinder and then transferred onto the paper. You will also notice that the image here is shown printed only in magenta. It is likely that the final output of this image would be in more realistic colors of blue, browns, and greens. This is only one pass of the paper. Each plate transfers a single color ink to the paper. It wouldn’t be feasible to transfer 10 solid colors for a single design, so the colors are separated into four colors–cyan, magenta, yellow, and black (CMYK)–and then applied on top of each other to create the full spectrum of colors. So, for a full color design the offset printing would actually print 4 separate colors on the paper that would mix to create the final product. If a design was created in just black and white there would only be one pass through the printer with black ink to print the full design all at once. This is why black and white printing is much less expensive than full color printing. It takes four times as long to achieve full color than it does black and white.
You’re probably thinking that this sounds like a more complex way of printing and may be wondering why everyone doesn’t use digital printing instead. Despite the complex nature of setting up offset printing it is extremely efficient in printing large quantities. If you are printing 500 or more copies of something offset will give you the lowest price. As your quantities increase, the price often doens’t increase much. So, if you’re trying to decide between printing 1,000 copies and 1,500 copies the price may be $800 and $850. The small margin of cost increase would make it more appealing to print more.