218 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
tory instead of being dug out of the earth; all other makeshifts being 
properly described as ‘‘imitations.” The production of imitation gems 
is by no means a modern invention, as is doubtless well known to you. 
To go no further back than the time of the Roman Empire, the master 
glassmakers of the dawn of our era, whose skill and knowledge of glass- 
making one appreciates more highly the more one investigates the 
industrial life of those times, were able to imitate almost any precious 
stone exactly, as far as outward appearance went, in colored glass— 
and not only the transparent gems, but the structure of such semi- 
precious stones as agate, cornelian, lapis, and porphyry. It would be 
quite out of place to devote any time to-night to this historical aspect 
of imitation gems, but I can not refrain from alluding to the remark- 
able examples of such imitations found by Mr. Woolley at Karanog,! 
from which it is difficult to resist the conclusion that in quite early 
times Nubia was the center of this industry. 'To judge by the stories 
one reads about jewels in those times—stories of the Emperor Com- 
nenus, for example—one suspects that the giassmakers turned their 
skill in this direction to some account and considerable profit on behalf 
of an ignorant and somewhat credulous aristocracy; for in those days, 
and, in fact, until quite recently, not only was the nomenclature of 
gems very vague, but methods of identification were chiefly remarkable 
for their nonexistence. 
The chief criterion of a precious stone was its color, so much so that 
throughout medieval times blue glass was known as sapphire and 
green glass as beryl, etc., giving rise to the legend that in the time of 
Queen Elizabeth windows were glazed with sheets of beryl.? As the 
tendency still lingers to regard all red stones as rubies and green as’ 
emeralds, and so on, I would like to make it clear at this point that’ 
color is really quite an accidental property of precious stones; the: 
substance of which nearly every species of transparent gem is essen-. 
tially composed is colorless, and the color is really produced by minute 
proportions of impurity. 
This being the case, we find that on the one hand the same species of 
gem stone may exist in a large variety of colors, and on the other hand 
that a color characteristically associated with one gem may often be 
found in another having essentially different composition and prop- 
erties. Owing to this confusion it was very difficult to draw the line 
between a genuine and imitation stone until the various species of gem 
stone were accurately defined and their names clearly associated with 
particular composition and properties, the determination of which 
forms at the present time a means of distinguishing one from another, 
1 Karanog, by C. L. Woolley and D. Randall. MacIver: Philadelphia Museum, 1910. 
2 This is quoted in Hollingshed. We read in Theophilus (II, cap. xii) of ‘‘tabulas saphiri pretiosas ac 
satis utiles in fenestris.””? Inaprevious paper (Journal, Mar. 15, 1907) I have shown how the name jet was 
variously applied. 
