On-press control of metallic inks

Investigations have been made to find practical measurements methods for metallic offset inks. Laboratory based tests and on-press tests were conducted utilizing a variety of metallic colors based on the Pantone® metallic book. The inks were tested in regards to polarized and non-polarized density measurements, gloss and color measurements using spherical and non-spherical spectrophotometers. 

Results showed that cyan density readings done with a polarized densitometer represented best changes in ink film thickness regardless of the tested color. Gloss measurements done at three different gloss angles showed that the 60° angle proved the most reliable. 

From the three colorimetric values L* indicated change in ink film thickness. L* measurements were conducted with a spherical spectrophotometer.

These three parameters were used to evaluate press sheets which were also analyzed for a visual match to the Pantone® book. From the three measurements, cyan density, gloss and L*, the L* value was in direct relation to the printed color in the Pantone book. L* measurements done with 0/45 geometry-based spectrophotometer gave a wider range in values, but were not as accurate as the spherical measurements in relation to a visual match.