Offset Printing

Offset printing questions and answers, from what is a bleed, to what is a reverse, to what are plates and how are they made.

Offset Printing Questions and Answers

Offset printing is a variant of the process developed by Gutenberg in the 15th Century. This process has undergone huge improvements over the ensuing centuries!

Offset printing is based on the idea that the image area to be printed should be transferred from a “plate” to a rubber blanket, and then to the sheet of paper. Offset printing is “wet” in that it uses a wet ink, usually either based on rubber or oil. At The Print Authority, we use oil based inks. If there are multiple ink colors, a different color is placed on each head of a press and they are transferred to the sheet of paper one color at a time. However, with modern multiple head presses, many ink colors can be transferred to the paper in one “pass” through the press.
The term digital printing can refer to processes taking place on one of many different types of equipment. Usually, digital printing refers to a device in which the image can be changed easily from sheet to sheet without changing plates or blankets. Although not a universal definition, most digital printers involve the use of dry toner or rapidly drying ink.

Offset printing is the best choice for documents with only a few originals and many prints of each original, while digital printing is best for documents with many originals and few prints of each original. Another differentiating factor is that although digital technology has made huge advances, offset printing typically produces the highest quality images available. On the other hand, digital copying can be the best choice for very quick turnaround jobs as digital printing is a dry process. Both digital printing and offset printing are employed at The Print Authority.

For more details on how to decide which process to use, call The Print Authority, at (615) 468-2679!
Spot color printing is offset printing in which specific PMS ink colors are used. With spot color printing, one can be precise about which colors will appear on the final printed piece.

Four color process printing refers to offset printing in which four set colors (cyan, magenta, yellow and black) are used to simulate most other colors. Four color process printing is also known as process color or full color printing. Although most colors can be simulated in four color process printing, one cannot be precise about the exact colors which will appear on a final printed piece. Four color process printing should be done on a press with at least four heads for the best quality results.
Proofing can vary greatly from printing company to printing company. At The Print Authority, we insist on proofing all offset printed jobs prior to printing, even ones which have been printed before.

For spot color printing jobs, proofs can be either simple black and white proofs or simple color proofs. For remote clients, a PDF of the final arwork can serve as a proof and an email reply can serve as proof approval. For four color process printing jobs, we frequently use a similar process. For full color offset printing, there is no advance proof which will produce exactly the same colors as the final printed piece.

For color critical projects, you can do a press check. In a press check, the client sees the first sheet off of the press. Once approved, we print the remainder of the project. Usually press proofs take about 15 minutes. If press checks involve more than minor adjustments, there may be additional charges.
Printing plates can be made from a number of materials, including rubber, polyester or metal. At The Print Authority, all of our plates are metal.

Before the onset of computer to plate (also called direct to plate, CTP or DTP), printing companies either generated negatives or paper (megalith) plates. These were generated photographically, by placing clean “camera-ready” copy on a graphics camera and shooting a “plate” or a negative. In the case of negatives, the negative and a metal plate were placed into a plate burner and the image was “burned” onto the plate. Then, the plates were developed chemically before use on the press. You can still find these systems in use, but they are being replaced.

Today, many printing companies, including The Print Authority, employ DTP systems in which the plates are generated digitally and come out ready to use on press. The Print Authority employs metal plates for all jobs, whether they are “spot” color jobs or process color projects. Metal plates are higher quality, do not stretch, and are best for fine detail, close registration or full-color printing.

The Print Authority uses a ‘Chemistry Free’ machine to produce metal plates. This machine produces no toxic chemicals requiring special processing. Further, we recycle 100% of our used metal plates.
Close registration means that two or more colors in a document either touch or are very close together on a sheet of paper. When colors are in close registration, they should usually be printed on press in one pass so that they are in the correct position with respect to one another. Four color process printing always involves close registration.
A screen is a shaded area on a printed page. Shaded areas are produced by converting an image into a series of dots. The dots lighten the color being printed.

One use of a screen is to simulate multi-color printing without using extra colors. Since screens lighten the solid color being printed, it is possible to achieve two different hues of the same color (for example, two blues) by printing the solid color and a screen of that color. Four color process printing combines screens of four colors to simulate other colors.

Halftones are printed representations of photographs. By using screens, it is possible to capture much of the detail contained in a photograph using either one or multiple colors.
There are many factors which determine the quality of a screened image or halftone. First, the quality of any printed photograph largely depends on the quality of the original image on the electronic file. Once the image is made a part of a document, whether it is a simple screen (shaded area) or a halftone (photograph), the quality of the printed area depends on the quality of the imaging on the plate machine being used, the number of lines of dots per inch (lpi), the size of the dots, the plate material being used, the quality of the press being used to print the job and the skill level of the press operator.

Metal plates produce a higher quality screened image than polyester plates, as metal plates show more detail and will not stretch during printing. One can create a screened area to print with anything from 50 lpi to way over 200 lpi. The higher the lpi, the crisper and smoother the image area. At The Print Authority, we can reproduce screens up to 250 lpi.
The term bleed refers to ink running off the edge of a page. The proper way to bleed an image is to run the image on a larger sheet of paper and then cut the paper after printing so the image runs off the edge of the sheet. The image on the electronic file must also run over the edge of the page to create a bleed.
Reverses are solid printed areas on a sheet containing unprinted type or images inside of the solid. In other words, the underlying color of the paper shows through in spots inside of the printed area. A good example would be a solid bar of color with words showing through in the middle, where the words are the color of the paper.

Reverses only become technically challenging when the underlying solid area is large or when the reversed area contains extremely fine detail. These can be challenging because the press operator must run a lot of ink to create a smooth looking solid area, but cannot run so much ink that the reverse disappears.
The term PMS ink color refers to the Pantone Matching System, which is a universal color matching system. Every PMS ink color has a corresponding number. There are thousands of PMS ink colors, and The Print Authority has a variety of PMS guides to show you how the final color will look on a printed piece.
No. Skilled spot color press operators always match the PMS guide to the PMS color at the beginning of a run, and then pull samples throughout the run to ensure consistency. Trying to match a PMS color AND an old printed sample from another press run is not a recommended practice. What was done on the prior run is uncertain while the PMS ink is a universal standard. If a press operator consistently uses the PMS guides for color matching, color should be very consistent from run to run.
Metallic inks are ink colors which contain metallic flecks, making these shinier than standard ink colors. Although most people think of metallic inks as being gold, silver or copper, there are also other colors, like blue, green and red available in metallic colors. These inks print like other inks except that they are more difficult to clean up on the printing press.
Although pricing philosophy varies from one printing company to another, ink colors usually cost more than black ink to print. There are two main reasons for a cost difference. First, colored inks typically cost more to produce than black ink does. Second, printing companies usually assume that black ink will be run every day since so many documents contain black. To run a colored ink, the press operator must “ink up” the press with that color and then must wash it up when the job is complete.
A coating is a type of clear covering which lays on top of the ink. This seals in the ink and protects the printed piece from fingerprinting and excessive handling. Coatings are most important for pieces which have extensive ink coverage or large solids.

Varnish is a simple clear coating which can be applied on press to seal in the ink colors. You cannot usually see varnish easily. Varnish can be either shiny or dull.

UV coating appears as a shiny clear coating which sits on top of the ink. You can feel UV coating as it is much heavier than varnish.

Aqueous coating is another coating which seals and protects.

Please call the experts at The Print Authority to find out whether a coating is a good idea for your next printing project!

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