Color is said to be one of the most important differentiators for consumer purchases, especially as the value of that purchase increases. As more durable and brilliant varieties of pigmentation technology become available, they are incorporated into automotive styling. Included in this variety of pigmentation are effect pigments, which are a broad category of materials consisting of metallic effect and pearlescent pigments. These materials have some unique capabilities with respect to how they interact with light, specifically due to their architecture (typically a platelet structure with a high aspect ratio). Depending upon the specific technology, a wide variety of colors and effects can be created, such as interference shimmers, color travel effects or metallic reflection.
Traditional pearlescent pigments consist of a high-refractive-index metal oxide layer coated onto a transparent, low-refractive-index substrate such as natural mica. This layering structure interacts with light to produce constructive and destructive interference patterns in both the reflected and transmitted light, which we see as color. This technology has been extended to other synthetic substrates such as glass, alumina, silica and synthetic mica. Various effects range from satin and pearl luster, to sparkle with high chromatic values, and hue-shifting color highlights, again depending upon the exact architecture (type of metal oxide, layer thickness, particle size distribution, aspect ratio of the substrates, etc.). When coated with titanium dioxide, these interference pigments range in color from silver, gold, red, blue and green. Additionally, iron oxide-coated substrates result in a deep chromatic luster effect. The main limitations of the pearl effects are lack of opacity and lower lightness contrast between specular and down flop angles.