268 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



which is the size of a small hen's egg. A few specimens of similar exceptional size are 

 known in Europe. Kaiser Rudolph II. of Germany possessed a ruby of flawless beauty and 

 of the size of a hen's egg, which was valued by the gem expert Boetius de Boot at 60,000 

 ducats (about ,£28,000). It is related that in 1777 Gustavus III. of Sweden presented to 

 Catharine II. of Russia a beautiful ruby of the size of a pigeons egg; the present 

 whereabouts of this stone is, however, unknown. The largest of the fine rubies set in the 

 French crown, according to the inventory made in 1791, weighed 7 carats, and was then 

 valued at 8000 francs (£320). Another weighed 25i^ carats, but on account of its pale 

 colour was valued at no more than 25,000 francs. Other rubies of large size will be 

 mentioned under the description of localities. The largest ruby known is said to be from 

 Tibet; it weighs 2000 carats, but is not perfectly transparent. The largest ruby yet 

 found in Burma is also a little cloudy ; its weight is given by Streeter at 1184 carats. A 

 tabular crystal of ruby of a rich red colour, and in part perfectly transparent, was presented 

 to the British Museum by Professor John Ruskin ; it has a weight of 162f carats. 



RcjBY AS A Gem. — The facets of a cut ruby are ground on a rotating iron disc 

 precisely as in the diamond. The use of diamond-powder as a grinding material is now 

 very general in Europe since it considerably expedites the process. The operation of 

 grinding is followed by that of polishing, which is effected on a copper disc charged with 

 tripolite moistened with water. 



The forms of cutting adopted for the ruby are those generally used for the diamond. 

 The brilliant form (Plate I., Fig. 6) is frequently chosen, since this displays the beauties of 

 the stone to the best possible advantage. In order to increase the transparency of the ruby, 

 however, the brilliant is cut thinner and flatter than is allowable in the case of the diamond. 

 Owing to the strong refraction of the ruby, the rays of light which enter the stone by its 

 front facets are totally reflected by the back facets and pass out by the front of the stone, 

 the fine red colour of the ruby having been imparted to them during their passage through 

 it. It is this colouring of the rays of light, together with the brilliant lustre of the stone, 

 which gives the ruby its effectiveness. Owing to the small dispersion of corundum, the 

 magnificent play of prismatic colours characteristic of the diamond is almost absent in the 

 ruby. This being so, the step-cut or trap-cut form of cutting (F^ate TH., Figs. 2 — 4) is just 

 as eff"ective as the brilliant for the ruby, or indeed for any coloured stone which shows no 

 play of prismatic colours. The mixed-cut, of which the upper portion consists of brilliant 

 facets and the lower those of the step-cut, is also an effective form (Plate III., Fig. 5). 

 Table-stones, point-stones, and similar forms are scarcely ever cut now; the few examples 

 met with are the work of former times. Flat and thin rubies are usually cut as roses 

 (rosettes), since this form involves little loss of material and, at the same time, produces a 

 good effect. Very small stones are irregularly faceted ; they are used to form a contrasting 

 border round some larger precious stone. 



In Burma, the chief home of the ruby, the stones are cut en cabochon, that is to say 

 with a rounded surface, before they come on the market. When this form of cutting does 

 not display the beauties of a stone to the best advantage it is re-cut in Europe. It is 

 obviously to the purchaser's advantage to buy a ruby cut e7i cabochon rather than an uncut 

 stone, since in the former case it will be possible to detect any faults in the interior. With 

 the exception of the asterias or star-rubies, this gem is seldom in Europe cut en cabochon ; 

 in the exceptional case mentioned, thl^ rounded form of cutting is obviously the most 

 suitable for displaying the six-rayed chatoyant star for which the stone is peculiar. 



Clear and transparent stones of a full deep colour are usually mounted in open settings 

 (a jour) ; those of poorer quality are often backed by a foil of gold or copper or red glass, 



