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FLEXO Magazine : October 2011
SPOT COLOR CHALLENGE The challenge in printing spot colors is the lack of density information provided to the press operator. CMYK colors have both ISO standards and specifications (FIRST 4.0) that suggest a density starting point. Spot colors are basically monitored by a visual check. Once ap- proved, the spot colors can be monitored using a densitometer. However, rarely do the colors have suggested density starting points. A flexo press has only a few controls that can directly affect color. Once the ink is at the press, the operator can increase or decrease density and make pressure adjustments. Monitoring colors on a press is done by use of a densitom- eter. A densitometer measures the amount of reflected light sent back into the unit. However, a densitometer measures density, not color. To monitor the specifics of a spot color requires a Spectrophotometer, which can measure color in a three-dimensional color space such as CIELAB or CIELcH. Spectrophotometers generate the information for these colors spaces by measuring the spectral data of the color. Spectral data is the color’s DNA. It is the measurement of the wavelength of the light reflected by the color, and can range from 400 to 700 nanometers. This is the visible light spectrum that corresponds to a range of electromagnetic radiation that can be detected by the human eye. Trending charts and color curves reflect the accuracy of printed spot colors. www.flexography.org ocTober 2011 FLEXO 71