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Methods & Processes
Clear vs. Chromatic Emulsion
Posted: May 6, 2008
page 2 of 2US Patent 5,290,555 to Guthauser et al., titled Cosmetic Compositions with Structural Color, issued March 1, 1994, gives the following explanation for this effect:
When two transparent, immiscible liquids are mixed, the combination is often cloudy. If, however, the liquids have the same refractive index , the mixture will be substantially transparent to the human eye and appear to be homogenous. The appearance of "structural color" in such a mixture requires not only that the refractive indices (at a given wavelength of visible light) are the same, but also that the variation of the indices as a function of visible wavelength differ for the two liquids. That is, the "dispersive power" of the two phases must be different.