Printing knowledge: Checking

A test is a quality control tool that is used to communicate the general concept of a project between a client and the printer. It is a large security measure designed to detect possible problems or errors before a job is printed.

A tie, or magnifying lens, is the best friend of bathers. It allows you to see the dot gain, overprint and ink saturation in your prints up close.

Applications

There is a wide variety of test systems and different technologies to choose from. It is important to understand the different processes and the advantages and disadvantages of each one.

Budget

All tests must include the following:

• Color bars

• Name, address and contact person responsible for the work.

• Date

• File identification

• Type of test (inkjet, print match, etc.)

• Purpose of the test (text only, color only, proof of contract, etc.)

• An area where approval or changes can be noticed.

• An area for the client's signature to indicate approval or acceptance.

Ink Jet / Digital Tests

Inkjet proofs require high quality glossy or coated paper for the production of photo realistic results. The paper itself is made up of two layers: the base layer is paper and the second layer is a coating that accepts the ink.

Digital tests are performed directly from the computer without creating a set of movies. Its quality has improved to a level that is acceptable for use as a final test.

When using digital systems for testing, it is necessary to calibrate the proofer often to maintain color accuracy, and color bars should be used in each test.

A digital proof process involves Catalogues Books Printing each of the primary color components subtractive to the image (cyan, magenta, yellow) and black in one pass through the output device to create the full-color digital proof as shown below.

Soft test

A color test on a computer monitor, which is based on the additive color process. PDF is the most common delivery format for screen tests, although JPEG files and other bitmap formats can be used.

While this test method is ideal for rapid changes during prepress, it is not accurate enough to be used as a final test. This is mainly due to the differences in the color range between the additive and subtractive color processes.

Match Print (halftone proofs)

The halftone proofs deliver such precise contract quality tests that match the press and can eliminate press controls. They are among the fastest and most accurate tests available in the digital domain.

Flat colors can be waterproofed on substrates and real points for accurate prediction of the printing process. The integrity of the image is also improved by controlling density and dot gain.

NOTE: Halftone printouts can be expensive and are usually reserved for projects where color matching and image quality are critical, such as reproductions of art galleries, books, magazines, presentations, etc.

Flat color

The colors used in direct color tests are also known as "combined" colors, special colors or by one of the brand names "Pan tone" or "PMS". Flat colors are printed with a single ink on a print unit separate from the press.

When choosing the spot color on the monitor, remember that it is simulated in RGB and not as the direct color or CMYK. Be sure to remove a chip from the guide and include it in the work.

NOTE: It is also important to keep in mind that the color guides fade over time and that the paper may change color, so check the date of your guide and replace it periodically.

Remember that if you try to match a spot color with process colors, very few colors will match. Many flat colors are out of the palette of process inks. The stock of paper and the use of varnishes or coatings can also change the appearance of the color.

Press tests

Press tests are the most accurate test method available, but they can be expensive. A press test involves the use of a press to generate a printed image before the execution of the actual press. It is mainly used to simulate printing processes using real plates, inks and paper.

Keep in mind that the price of work may include an additional press installation fee due to the time it takes to produce the press test and then reconfigure the press when the time comes to produce the actual work.

Composite superposition test

One of the trade names for a composite overlay test is Color Key ™ (Kodak). Each layer is a separate color that overlaps each other. The layers are glued with adhesive tape to any material to be registered with the other layers and are generally placed in the order in which they will be printed on the press.

The composite overlay test can be useful for checking color breaks, trapping, text and design, but it is not suitable for matching colors in the press. The illustration above shows how the four layers, representing the process colors, are recorded so that the individual layers can be recorded.

Integral composite test (percolated subtractive)

An example of a filtered subtractive test is Match Print ™ (Kodak). A negative for each color is placed on a laminated colored sheet, exposed to ultraviolet light and then processed. Consistent densities, dot gain and color are the main advantages of this type of test.

Blue line

Sometimes called Dylex, it is a one-color test made of the four separation films. It is used to verify the imposition, the text, the design and the traps, but it is not used to verify the color.

Most systems use a vacuum frame to hold the film or the plane in contact with the coated sheet sensitive to light. A source of ultraviolet light then exposes the emulsion to create the image. There is no processing involved. It can be folded, cut and sewn to approximate the finished work. The test is bluish in color and the image fades over time.

Sometimes called Dylex, it is a one-color test made of the four separation films. It is used to verify the imposition, the text, the design and the traps, but it is not used to verify the color.

Most systems use a vacuum frame to hold the film or the plane in contact with the coated sheet sensitive to light. A source of ultraviolet light then exposes the emulsion to create the image. There is no processing involved. It can be folded, cut and sewn to approximate the finished work. The test is bluish in color and the image fades over time.

Scatter Proof

A test of an individual photo or a group of photos that have not been included in the complete design of the page. Several photos can be grouped and corrected at the same time to save time and materials.

Looking at Booth

Regardless of the test method you choose, it is vital to see them under the right lighting circumstances. Any worthwhile printer will have an observation booth to match colors with the highest precision.

Contract or final test

A final test serves as a legal contract between the producer and the client, once the approval of the test has been signed. The customer must understand that it does not represent the exact appearance of the print sheet, since the proof paper is often brighter than what is used in the actual print and almost always has a higher image density than the one that can be delivered a press.

The test of the contract only simulates and predicts the appearance of the final printed piece. It is used in the press room as a guide to compare colors while the piece is running in the press. A proof of contract can be produced as:

• A photomechanical (analog) film test

• A digital proof of a digital file

• A press sheet as a press test