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Color Characteristics of Optical Variable Pigments and Their Measurement Standards & Instruments


The color of optical variable pigments (OVP) exhibits the characteristic of goniochromism, meaning that the observed color varies with different viewing angles. Therefore, accurate color analysis of optical variable pigments requires the assistance of specialized color measurement instruments. This article introduces the color measurement standards and instruments for optical variable pigments.

colorful optical variable pigments


Color Measurement Standards for Optical Variable Pigments


Current quality evaluation standards for optical variable pigments and their related printed products are mainly divided into two categories:

  • ASTM E2194: Recommended for measuring metallic pigments where goniochromism is primarily caused by scattering.

  • ASTM E2539: Recommended for measuring pearlescent pigments or film-changing pigments where goniochromism is mainly caused by thin-film interference.

ASTM E2194 specifies the measurement angles for metallic inks, stating that measurements at three angle sets—r45as15°, r45as45°, and r45as110°—can effectively characterize the color-shifting effect of metallic pigments. Published in the same year, ASTM E2539 further refines these specifications by defining the measurement geometries for interference thin-film optical variable pigments. It stipulates that goniochromism caused by thin-film interference should be measured at four angle sets: r15as15°, r15as-15°, r45as15°, and r45as-15°. Additionally, building upon ASTM E2194, it expands the angles for measuring color changes caused by scattering by adding two more sets—r45as25° and r45as75°—to enhance measurement accuracy.
The Chinese national standard GB/T 17001.7-2023 "Anti-counterfeiting Inks - Part 7: Optical Variable Anti-counterfeiting Inks" includes relevant methods and evaluation criteria for surface color measurement in its Chapter 7. This standard specifies the color measurement requirements for optical variable inks. Based on measurements and analyses of samples from multiple manufacturers using multi-angle colorimeters, it concludes that the color-shifting characteristics of optical variable inks can be effectively characterized by measurements at r45as45° and r45as-15°.

Color Measurement Instruments for Optical Variable Pigments

A variety of instruments are available on the market for measuring the color of optical variable pigments, with multi-angle colorimeters being the primary choice. We recommend the 3nh Multi-angle Spectrophotometer KS600, which features an innovative configuration of 8 light sources and 1 receiver, enabling simultaneous measurement at 6 angles to comprehensively capture the goniochromic characteristics of metallic, pearlescent colors.
Its measurement angles cover 45as-15°, 45as15°, 45as25°, 45as45°, 45as75°, and 45as110°, meeting full-scenario observation needs. The instrument is perfectly suited for measuring complex and special-effect colors such as metallic, pearlescent, and solid colors, solving traditional measurement challenges. It can directly measure sparkle, color sparkle, and graininess, replacing traditional subjective visual evaluation with standardized quality inspection. The short-term repeatability is 0.11% for sparkle and 0.08% for graininess (average of 10 measurements on BCRA color tiles at 10-second intervals).
As the viewing angle changes, the color of variable pigments varies significantly. The KS600 spectrophotometer conducts quantitative color analysis of variable pigments from multiple angles:

  • The 15° viewing angle, close to specular reflection, is ideal for measuring high-gloss colors.

  • The 110° viewing angle, far from specular reflection, reveals the diffuse reflection color of the sample, i.e., the inherent color of the pigment.

  • Color difference measurements at 15° and 25° primarily reflect lightness differences.

  • Color difference measurements at 75° and 110° mainly indicate hue deviations.

  • Since 45° is the optimal angle for human color perception, measurements at this angle best reflect human visual effects.

Typically, color difference measurements at 25°, 45°, and 75° are used as the key indicators. First, input the chromaticity values of the standard color sample into the colorimeter as the reference. The subsequent measurement results will show the color difference between the measured point on the object (e.g., vehicle body) and the standard sample.


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