Measurement and Visual Evaluation of Metallic Gloss of Prints

Metallic gloss is increasingly used for simulating high quality of a product. Since the methods used for producing metallic gloss widely differ, e. g. bronzing, offset, gravure and flexo-printing, they also effect a different appearence. Therefore it is desirable to have a measuring technique at hand the application of which allows to numerically specify the size of the visually perceived metallic gloss. Using gonio-spectrophotometry, it is possible to evaluate colour and lightness of the light reflected from metallic prints at different angles. Plotting the lightness and/or the colour values of the reflected light as a function of the measuring angle results in an indicatrix, the form of which is given by the character and strength of the gloss of prints. Using this measuring technique, metallic gloss can clearly be differrentiated from surface gloss and the ranking of the visually perceived metallic gloss of a variety of printed samples could be confirmed by the measurement results.