Indian Beautiful Bridal Jewelley Collection 17

Indian Beautiful Bridal Jewelley.

By Aamir Mannan.

These reflectivity meters aim to identify gemstones, where these have a clean and well polished table facet, by measured their reflecting power when a narrow bean of infra-red light impinges on this facet.

Such instruments have certain distinct advantages over the traditions types of jeweller's refractometer that have been the mainstay of gems identifications for three-quarters of a century.

But they also have grave limitations, which are explained later in this chapter.

The refractometer in still an essential instrument for the gemmologist, and the principles of its constructions and hoe to make the best use of it are fully explained later.

First, however we must explain the meaning of refraction and refractive index and the basic principles on which the refractometer operates.

What happens when a ray of light fall on the surface of a transparent solid such as a gemstones or a sheet of glass? Some of the light is reflected at the surface of  the stone.

The reflected  light leaving the surface at an angle equal to that at which it falls upon the surface ('incident angle' or 'angle of incident').

It is the reflected light which provides the surface lustre of the stone.

The greater proportions of the light, however, passes into the stone, but in this dencer medium it travels much more slowly than in air.

The effect of entering the dencer medium, in which their velocity is diminished, upon trains of light waves striking the surface obliquely is to alter their direction and make them follow a new path nearer to the perpendicular (or 'normal' as it is called) to the interface between the two media.