The properties of precious stones

B J Tully
1909 Transactions of the Optical Society  
Delivered o n Becember 1Gth, 1909. MR. B. J. TULLY had k e n announced t o lect u r e on the optical properties of precious stones, b u t he apologised a t the outset by saying that he had k e n under some misapprehension in the matter of the subject, and although the optical side would be dealt with, he would deal more generally with the properties of precious stones. A11 precious stones, he said, to the exclusion of pearls, were of mineral origin. They were selected for their beauty and
more » ... ir beauty and rarity, and the quality of possessing suffircient durability t o render them suitable f o r purposes of personal adornment. They were sub-divided as precious and semi-precious, although there was no definite line of demarcation. The lwauty uf a gem was not manifest until the cutting nnd polishing had been carried out. Then its individual colour and lustre k a m e apparent, and it was upon the degrees of colour and lustre that the value depended. Beauty niiglit depend upon both colour quality, as in the c8se of the rich ruby, o r on total absence of colour as in the pure white diamond. The property of hardness was of vital importance, and it was this attribute which rendered the stone able to withstand attrition ancl knocking about by the wearer. The beaut1 of a great niany precious stories was ruined by rough and improper usage. Rarity was governed by supply ancl deriiand. and only those stones which coinl>ined p e a t beauty and rarity and high degree of durability laid claim t o the title of l i precious." The average person was probably acquainted with eight or ten varieties, but as a matter of fact there mere eighty to one hundred varieties
doi:10.1088/1475-4878/11/1/303 fatcat:e4sobomrtrg65prdbodzucbtsa