Plate Measurement

Q. Can I use my X-Rite densitometer to verify dot area on printing plates before going to press? A. Yes. Your densitometer can be used to measure, correct, and control your plate imaging process. To get the most out of using your densitometer in this way, consider the following factors. The Densitometer’s Forte The first thing to keep in mind is that, color reflection densitometers are designed to read the amount of incident light absorbed by a photograph, press sheet or off-press proof. As a result, these densitometers are designed to accurately measure Black, Cyan, Magenta, and Yellow colorants on a substrate like paper. YES YOU CAN! X-Rite has successfully measured dot area from exposed and processed lithographic offset plates – conventional and digital alike. In addition, comparisons made by leading plate manufacturers have found X-Rite densitometers to be doubly useful. In addition to measuring a variety of plate materials with consistent and reliable results, these manufacturers have used the same instruments to also measure their proofs and press sheets. Offset lithographic plates, however, do not usually have cyan, magenta, yellow, or black images on a white substrate. Instead, the plate material is usually brushed aluminum with a gray color. The color of the image area varies with the plate type and manufacturer; typical colors include green, pink, brown, black and blue. Polyester-based digital plates are nearly the inverse of ink on paper—a near-white image on a flat black sustrate. These color properties introduce unique issues that arise when the plates are evaluated using densitometers. Contrast As a result of plate color properties, the contrast between the image and non-image areas of the plate may be less than ideal. Plate contrast is typically less than half that of ink on paper. In fact, some plate materials do not exhibit enough color difference between image and non-image areas. As a result, the densitometer may not be able to calculate the exact dot area imaged