Figure 4: a set of selected loci for two arbitrary coating materials with refractive indices 1.4 and 2.2, respectively. For each material, there are an infinite number of loci for any particular wavelength and they do not intersect. The design of Figure 3 is superimposed in bold: notice how the design jumps from one locus to another (starts a new layer) to allow intersection with point (1, 0).