282 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



In the manufacture of the so-called ruby-glass various pigments have been used for the 

 purpose of reproducing the colour of the ruby. Manganese salts give a fairly close 

 imitation, but the colour which results from their use is too strongly violet. The best 

 results are obtained with gold salts, purple of Cassius, &c., which are fused with the glass or 

 strass. The use of gold salts necessitates the greatest care, otherwise the glass will be cloudy. 

 A glass coloured with gold salts after first being cooled is yellowish-green, the fine red 

 colour only appearing after the glass has been annealed, an operation which is known as 

 " tinting." By the use of gold salts, glass of the finest ruby-red colour can be obtained, and 

 by varying the percentage of gold in the strass different shades of colour are produced. 

 It is an interesting fact that fine ruby-glass has been found in ancient Celtic graves. 



SAPPHIRE. 



Characters. — Sapphire (" oriental sapphire ") is the name given to blue corundum. 

 Sapphire differs from ruby most essentially in colour, it is in addition, however, slightly 

 harder, being the hardest of all the varieties of corundum ; and, moreover, is stated to have a 

 slightly higher specific gravity, the specific gravity of ruby being given as 3"99 to 4'06, and 

 that of sapphire as 4"08. The form of a crystal of sapphire agrees completely in its general 

 symmetry with that of a crystal of ruby. ; the two crystals diflfer somewhat in habit 

 however. The prism and rhombohedron, usually well developed in the ruby, are subordinate 

 in the sapphire, and here the hexagonal bipyramid predominates, as is shown in Fig. 53, 

 e~i, and for a natural crystal in Plate I., Fig. 7. 



While the ruby is usually coloured uniformly throughout its substance, the distribution 

 of colour in the sapphire is often very irregular. A single stone may show an alternation 

 of colourless, pale yellowish, and blue portions, or in the colourless ground-mass of a stone 

 there may be patches of a blue colour. Such stones, compared with a sapphire of a uniform 

 blue colour, are almost worthless as gems. 



It would be quite possible to collect a series of sapphires showing small gradations in 

 colour from deep blue to yellowish or colourless stones. These latter are known as lehiie 

 sapphire (leuco-sapphire) ; they are only rarely perfectly colourless and transparent, usually 

 showing a bluish or yellowish tinge. Sapphires of a definite yellow colour are described as 

 " oriental topaz.'' 



The blue colour of the sapphire disappears on heating, hence it is possible to transform 

 a patchy or pale-coloured stone into a leuco-sapphire, and at the same time greatly enhance 

 its value. 



The distribution of the blue patches in the colourless or yellowish ground-mass of a 

 sapphire is usually quite irregular, only occasionally is there any definite arrangement to be 

 observed. In such cases, the crystal may be blue at one end and colourless at the other, or 

 the middle portion may be colourless and the two ends blue, or colourless and blue bands 

 may alternate. Moreover, different portions of the same specimen may exhibit different 

 shades of blue, such as pure blue and the greenish-blue peculiar to the sapphires of Siam, or 

 even colours which are altogether different. Thus, crystals of sapphire are known which 

 ai-e blue at one end and red at the other, and others of which the two ends are blue and the 

 middle part yellow. A crystal answering to this latter description and weighing 19^ carats 

 is exhibited in the mineralogical collection in the museum of the Jardin des Plantes in 

 Paris. 



The peculiar distribution of colour in such sapphires has been sometimes ingeniously 

 utilised ; for example, the figure of Confucius, preserved in the museum at Gotha, is carved 



