Emerald Bridal Girls Jewellery Collection 21- 2013

Emerald Bridal Girls Jewellery.

By Aamir Mannan.

There is a point here which may usefully cleared up since it causes confusion to students. what is known as the critical angle of a stone is the angle at which rays of light passing from the stone into air are refracted at 90 to a line prependicular to the surface between the two media . rays striking the inside surface of a stone at angle creater than this critical angle cannot emerge, and are totally reflected back into the stone. here the stone is the denser medium, and the higher the refractive index of the stone is the smaller is its critical angle. in the case of refractomemter the principle is exactly the same, but here the glass of the refractometer is the denser medium, and the stone is the rarer medium. thus, in this case the higher the refractive index of the stone the greater is the critical angle between it an the glass of the instrument.When a doubly refractive stone is too small or has to low a

birefringence to show doubling at all easily by the straight forward lens inspections describe above, another simple but more sensitive technique may yield valuable information. this has been practised indipendently in the past by max bauer, G.O. Wild, G.O. crowning shield and R.K. Mitchell, and in recent years has been systematiesd into a routine process of visual optics by alan hodgkinson, who uses it with exceptional skill and success.  The method is best applied in a darkened room with a single light source, which may be either a clear electric bulb with 'C' filament or (more conveniently) a small 'slit' torch of the type produced by hanneman lapidary specialist (figure 3.2). the stone to be examined, if large or mounted with an open baking, can be held in the hand, or if small in tongs.

By Aamir Mannan.
There is a point here which may usefully cleared up since it causes confusion to students. what is known as the critical angle of a stone is the angle at which rays of light passing from the stone into air are refracted at 90 to a line prependicular to the surface between the two media . rays striking the inside surface of a stone at angle creater than this critical angle cannot emerge, and are totally reflected back into the stone. here the stone is the denser medium, and the higher the refractive index of the stone is the smaller is its critical angle. in the case of refractomemter the principle is exactly the same, but here the glass of the refractometer is the denser medium, and the stone is the rarer medium. thus, in this case the higher the refractive index of the stone the greater is the critical angle between it an the glass of the instrument.When a doubly refractive stone is too small or has to low a birefringence to show doubling at all easily by the straight forward lens inspections describe above, another simple but more sensitive technique may yield valuable information. this has been practised indipendently in the past by max bauer, G.O. Wild, G.O. crowning shield and R.K. Mitchell, and in recent years has been systematiesd into a routine process of visual optics by alan hodgkinson, who uses it with exceptional skill and success.  The method is best applied in a darkened room with a single light source, which may be either a clear electric bulb with 'C' filament or (more conveniently) a small 'slit' torch of the type produced by hanneman lapidary specialist (figure 3.2). the stone to be examined, if large or mounted with an open baking, can be held in the hand, or if small in tongs.