SYNTHETIC BLUE SPINEL STONE
By Aamir Mannan.
Cobalt-blue is never found in natural minerals and when seen heralds the presence of some artificial product-notably blue synthetic spinal or cobalt class. The cobalt absorption bands seen are very similar in each case, consisting of three broad bands in the orange, yellow and green, but in synthetic spinal the bands are more closely clumped
together (see drawing) and the central band is widest of three, whereas in the glass the center band is the narrowest. Wavelength of the synthetic spinal bands are 6350, 5800 and 5400 A. The width and intensity of these bands vary proportionately to the depth of the blue colour. In deep blue specimens the bands almost
amalgamate into a single block. Absorption of the yellow green, together with free transmission in the deep red make these cobalt-coloured artifacts appear strongly red under the Chelsea filter.
By Aamir Mannan.
Cobalt-blue is never found in natural minerals and when seen heralds the presence of some artificial product-notably blue synthetic spinal or cobalt class. The cobalt absorption bands seen are very similar in each case, consisting of three broad bands in the orange, yellow and green, but in synthetic spinal the bands are more closely clumped together (see drawing) and the central band is widest of three, whereas in the glass the center band is the narrowest. Wavelength of the synthetic spinal bands are 6350, 5800 and 5400 A. The width and intensity of these bands vary proportionately to the depth of the blue colour. In deep blue specimens the bands almost 
amalgamate into a single block. Absorption of the yellow green, together with free transmission in the deep red make these cobalt-coloured artifacts appear strongly red under the Chelsea filter.
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