Essence d’Oriente

Natural pearl essence (Essence d Oriente, Fish Silver) is a pigment suspension derived from fish scales, skin, or bladder. It is the oldest commercial pearl luster pigment, consisting mainly of a mixture of the purines guanine [73-40-5] (75-97%) and hypoxanthine [68-94-0] (25-3%). 

Mica can be used today instead of essence d orient. Tiny flakes of the material are suspended in a synthetic resin and applied in the same way. 

Other compound coatings. A number of other compoimds can be induced to crystallise in a submicroscopic platelet form imitating aragonite, and suspended in a variety of lacquers or resins, which can be applied in the same way as essence d orient. 

The above interpretation is, in essence, the result of the limiting case of Eqs. (D.15) and (D.14), as may be confirmed by comparison between (D.47), (D.48) and (D.31). It will emerge that in the classical limit the total population nj will be replaced by the total probability W, and the normalizing factor (2J + l)-1/2 will be replaced by (4 r)-1/2. The latter replacement is due to the fact that, in passing from the quantum to the classical approach, the number of possible spatial orientations of the angular momentum, equalling 2J + 1, must be replaced by the full solid angle 4n. 

While the specifics of the NBG model can be somewhat involved [15], it is in essence an intuitive model of two coupled oscillating dipoles. One dipole is associated with either an electronic or nuclear transition moment of the molecule. The other dipole is chosen to be consistent with the SP excitation of the metal nanoparticle. Let the metal nanoparticle of radius a be at the origin and let the molecule lie on the positive z-axis a distance d from the nearest surface of the metal so that a + cl is its distance from the origin, as in Figure 9.1. For simplicity I assume both the molecular uansition dipole and SP dipole are oriented along the z-axis. Let the z-components of the molecular and SP dipoles be denoted by fi and p respectively. The NBG model is then... 

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