The Fogra research report 52.040 K quantified the metallic character of golden metallic print products from different printing processes (offset with metallic effect pigment, printed metallised papers, hot stamping foils).
Wet glue labels and folding cartons were used to analyse golden metallic patterns from packaging printing. Printing processes such as offset printing with different metallic pigments (coated and uncoated), offset printing on metallised substrates and hot stamping foils were used to create the metallic effect. A large number of physical measurement values were determined for the samples. Using a multi-angle measuring device, colour and brightness data could be determined for different detection angles and it turned out that measurements in the immediate vicinity of the mirror angle are not possible. Another measuring device used was a sphere spectrophotometer, which was used to determine SPI (‘Specular Percentage Index’) parameters, which indicated the proportion of reflected light in relation to the total amount of reflected light. As gloss plays a significant role in the perception of metals, this was also measured using a gloss meter, which was used to determine aspects of multidimensional gloss perception.
The visual assessment of the samples was carried out in six groups of six samples each by ten test subjects under parallel directional and diffuse lighting. The psychological data were first used to determine the evaluation figures for the samples within a group and then to form an overall evaluation. The intensity of the metallic character resulted in the following order: offset samples (coated and uncoated) < semi-matt hot stamping foils < printed silver papers < glossy hot stamping foils. Physical parameters that correlate with the visual evaluation could be determined with almost all measuring devices.
Overall, it was found that the appearance of metallic samples differs from dielectric materials in terms of gloss properties, brightness values and changes in brightness near the mirror angle. When looking at the samples, a gradation was found for the intensity of the
metallic character between patterns from different printing processes. The gradation is pronounced between the group of offset patterns (coated and uncoated) and the other patterns (printed silver papers and hot stamping foils). Finer differences, such as those occurring within the offset sample group, could not be resolved within the scope of the project. This is due to the fact that the evaluation scale was applied to samples from different printing processes and therefore has a relatively coarse resolution.
Fogra
Fogra conducts application-orientated research in the fields of print and media technologies and has often been able to create standards for processes and quality testing. Fogra’s international members are companies from the entire industry spectrum, from the production of print and electronic media to plant engineering. Fogra sees itself as a modern service provider that carries out meaningful tests and certifications, advises companies on quality issues and mediates in technical disputes. Its capital is a wealth of expertise combined with a high level of technological competence and precise knowledge of current developments.
