Over the decades, modern offset and web printing (not to be confused with web-to-print) have used standards for color, ink densities, and best practices in order to achieve consistency from job to job, and, even in the competitive environment, printer to printer. Universal terms such as PMS (Pantone Matching System), and standards of paper measurement – for example basis weight, points, grams per square meter (GSM) – have allowed for a unity in both how clients specific printed product, and how printers have been able to consistently provide correctly printed jobs. However, there are additional standards that printers use as means of creating consistency within their environment in color, and on the press. Those are SWOP, GRAcoL and the newer G7. These are all measurement standards, and in some cases, printers have to become certified in order to use these specific standards. For example, a shop can be G7 certified, but it can also have a G7 Certified Experts or Masters. Let’s explore those three distinctive standards and how they are applied.
SWOP is an acronym that means Specification for Web Offset Publications. It is the standard used by web printing houses, which publish magazines, catalogs and books. This SWOP standards cover inks used (CMYK), which are specifically formulated for the web-printing process. SWOP covers the proofing methods so that the proofs match what will be printed on the press sheet. SWOP specifies acceptable dot gain, and how to produce halftones or 4-color images. It also creates constraints as to minimum font size, fonts in a reversed-out area, the amount of ink coverage on a specific area of the sheet, and and it sets up color profiles which are in compliance with the ICC (International Color Consortium). SWOP is a voluntary organization that requires certification, but web printers who print product for wide distribution in various markets, and who have multiple print plants in the USA use it to insure consistency from plant to plant.
GRAcoL is also an acronym for General Requirements for Applications in Commercial Offset Lithography, and it specifically applies to sheetfed printing, not web printing. GRAcoL certification address inks, which must meet certain ISO standards, which must be printed on what are called #1 or #2 sheets. #1 sheets are premium, usually “virgin” paper made from wood content, whereas #2 sheets are made from mix of wood and post-consumer waste pulp, and are often milled in east Asia. GRAcoL came about less than 20 years ago through a consortium that wanted to create standards that ensured consistently printed products. Printers could adopt these standards as a means to have accurate color from job to job, or one side of the press sheet to the other. GRAcoL 7 is the newer version of the standard, which expanded the process into the proofing and plating system, using a gray-balance as means of calibration. However, GRAcoL 7 applies only to #1 sheets.
G7 – the newest standard
The newest standard for sheetfed print production is G7, based on principles of digital imaging, spectrophotometry, and computer-to-plate (CTP) technologies. G7 can be used across multiple print methods, including commercial and publication printing, newsprint and even flexo. G7 requires printing with inks that fall within a certain ISO. The goal is to specify a calibration process that will enable the print provider to consistently achieve a close match from proof to press. The concept behind G7 is that it focuses on colorimetric data for gray balance in the mid-tones rather than on densitometric aims, i.e. dot gain, for each color. G7 uses a standard of gray for calibration of proof to press, and ink densities on the press sheet. G7 is also an acronym that is a bit confusing: the G stands for “gray”, and the 7 indicates the seven colors used to achieve the calibration (the four primary colors and three 2-color overprints specified in the specific ISO). Constant testing and calibration is done to insure that proofs and press sheets will match, and shops can be certified as G7 shops, and prepress operators can also be certified as G7 Experts or Masters.
You can find much more detailed information on the website for IDEAlliance, the organization for SWOP, GRAcoL and G7 certifications.