Remember when you were a kid and you pressed a little slab of Silly Putty against the comics section of the newspaper? What you saw when you turned the Silly Putty over was a reproduction of a comic, only it was backwards. And if the ink coverage on the comics was heavy enough that day, you could press the Silly Putty back onto a piece of paper and get a reproduction of the same image.

So explains the offset printing process.

Simply put, the offset printing process is a series of reproductions from a positive image to a negative image. There are as many as five such reproductions necessary to produce the type of product that DFW Printing Company, Inc. runs every day-a newspaper.

The first step in the process is to produce a positive image of what is to be reproduced. This is usually a page of type and graphics that is affixed on a flat, card-stock surface, typically known as a “board.” The type is black, the background is white. The board looks as closely to what the actual reproduction is supposed to look like, with the exception of any text or graphics that requires special handling.

In the second step, the board is then photographed to make a negative, similar to which is used in your typical camera at home. The image is exposed by light onto a silver-based film that is smooth on one side and emulsified, or rough, on the other. On the negative, all that is white on the board is black, and vice versa. Once the negative is cleaned and opaqued as necessary, it is ready for the third process-platemaking.

On the surface plate, the same image as on the negative is exposed through ultra-violet light, only in a positive or right-reading display. Surface plates have an aluminum base metal and a light-sensitive coating which is removed from the non-image area after exposure either through either a negative or positive. All that is white on the negative is exposed as black on the plate. The exposed black image, or image area, on the plate is made up of a material that is grease-receptive and water repellent. The non-image area, or all that is left unexposed, is made up of a coating that is water-receptive and grease-repellent.

The fourth step of the process happens in the pressroom, when ink meets the plate and the plate meets the blanket. On press, both a water-based dampening solution and greasy ink are applied to the plate as it rotates on the plate cylinder. The ink sticks to the grease-receptive image on the plate, while the dampening solution prevents ink from sticking to the non-image area. The image, inked and cleaned, is transferred to a blanket cylinder which touches the plate as the press is running. The blanket, which is made up of a rubber-like, absorbent material much like the Silly Putty, absorbs the ink off the plate and turns the image back into a negative.

The fifth and final process is when the blanket transfers the inked image onto the paper. As the paper touches the blanket, the image is impressed or offset onto the paper. There, the final image is returned to a positive, right-reading display. And now the page is ready for you to read!

There are five important advantages to the offset process in lithography printing:

• The rubber printing surface (blanket) conforms to the irregularities of the paper surface. Less printing pressure is needed so that halftones of good print quality can be obtained on rough-surfaced papers.

• The paper does not contact the aluminum plate, which reduces abrasive wear and increases the running life of the plates.

• Printing speeds are increased.

• The image on the plate is right-reading, rather than reversed, which facilitates both the preparation of the plates and correction of errors.

• Less ink is required to obtain equal coverage. Use of less ink improves color trapping, speeds up ink drying and reduces smudging and offsetting.