Pearlescent optical effects

Metallic, pearlescent and fluorescent pigments are grouped together in this section as three types of pigment used for their ability to produce unusual optical effects. 

There is an interesting and diverse range of pigment types which have the ability to produce novel and unusual optical effects in application. These products, which include metallic, pearlescent,... 

Synthetic or natural pigments used to achieve lustrous, brilliant, or iridescent color effects by interference on thin optical films are called nacreous or pearlescent pigments [5.190]—[5.194]. They were originally used to simulate the appearance of... 

In order to understand how three distinct colors from one pigment are possible, it is first necessary to understand the optical properties of pearlescent and interference pigments and also the optical properties of absorption colorants. The manner in which these reflect light differs and this forms the basis of the three color effect. 

This difference in refractive indices, arising equally on the interface between air/ oil film or oil film/water, is a prerequisite for the well-known iridescent color images in these media. Small highly refractive platelets of pearlescent pigments align themselves parallel in optically thin systems such as paints, printing inks, or plastics. Interference effects develop when the distances of the various layers or the thicknesses of the platelets have the right values. 

The physical background of optical interference effects has been the subject of many publications [3-8, 43, 44]. The optical principles of pearlescent (interference) pigments are shown in Figure 7.2 for a simplified case of nearly normal incidence without multiple reflection and absorption. At the interface P, between... 

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