30 
j. h. boas: 
The Federal Capital Site. By J. G. Hay. 
(Read September 12th, 1911). 
A Description of some Artificial Re-constructed 
and Synthetic Gems. By J. H. Boas, B.Sc. 
(Read October 10th, 1911-) 
ABSTRACT. 
The author first defined the following terms : — 
Artificial gems are laboratory products which 
simulate the appearance of but have not the 
specific properties of natural gem stones. 
Reconstructed gems are laboratory products made 
by fusing broken or imperfected stones into 
larger and more perfect gems. 
Synthetic gems are made by chemical processes 
and have not only the appearance, but also' 
the specific properties of the natural stones. 
The main methods of imitating gems were describe^, 
including the various forms of doublets, paste gems, and 
natural stones substituted for more valuable gems. Some 
types of doublets were exhibited. 
A description of those properties most valuable for the 
exact determination of the nature of gems was then given, 
together with an account of the Herbert Smith refractometer 
and the dichroscope. The use of these instruments was de- 
monstrated. 
The main portion of the paper dealt with the manu- 
facture of reconstructed and synthetic rubies and emeralds, 
together with the results of many examinations of the 
specific properties of these gems. The most recent method 
for the manufacture of these stones by Verneuil’s method 
of fusing the finely powdered mineral or its equivalent, pure 
alumina, together with the proper amount of colouring 
matter, in properly designed oxyhvdrogen blowpipes, was 
described. 
Pure alumina fused in this way gives white sapphires. 
The addition of tiny quantities of chromium oxide yields 
the ruby. For many years attempts to obtain the blue 
colour of the sapphire failed because oxide of cobalt was 
used as the colouring agent. This fails to combine with 
the alumina unless magnesia is added. The result, however, 
was the formation of blue spinels, differing entirely in pro- 
perties from the sapphire. Within recent years the use of 
oxide of titanium has led to the manufacture of sapphires, 
but the colour of the stones is not really good, and they 
can be readily detected from natural sapphires. 
