What is the Color Bar on My Proof?

Do you ever receive a proof and wonder why there is a bar of color at the bottom or on the side and what it could possibly mean? A color bar serves an important function in achieving consistent color and quality on press. A color bar is a test strip composed of three sections: Solid Ink Patches, Tint Patches, and Solid Color Overprints. Each section measures different aspects of the job.

Solid Ink Patches — as the name implies, are patches of 100-percent ink color used to print the job. For example, if your job is printing in 4-color ink you will see solid ink patches that represent cyan, magenta, yellow, and black at 100-percent value. The solid ink patches are used to read hue and grayness (to ensure the purity of the ink from the manufacturer) and to take density measurements. Ink density is measured to ensure color quality and consistency throughout the job. Measuring ink density tells the press operator how much ink is being laid down on the press sheet. Throughout the print job, a press operator will take measurements to make sure the job is printing up to color.

Tint Patches — are screened patches (less than 100-percent value) of the ink color used to print a job. Our tint patches can be 25-, 50-, or 75-percent screens of the color. If your job is printing in 4-color ink, you will see tint patches in the color bar that represent cyan, magenta, yellow, and black screened at the appropriate percentage value. The tint patches are used to measure dot gain, a phenomenon that occurs on press when the dots composing an image increase in size. The outcome is a darker or stronger color or tone that could result in less contrast or detail than desired. Dot gain is not necessarily bad as long as it is controlled. We control dot gain through such adjustments as print curves, plate curves, total ink limit, and line screens.

Solid Color Overprints — are patches used to gauge ink trapping. Ink trapping, in this instance, refers to the relationship of the inks to one another as they are laid down on the press sheet. The press operator uses these patches to measure the ability of the first ink color to accept or adhere to the second ink color; in other words, the tackiness or stickiness of the inks. The inks need to trap or stick to each other correctly for the press operator to achieve accurate color. In a 4-color job, you would see red, purple, and green solid color overprint patches.

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