322 NATURE 
[JANUARY 31, 1,907 
behaviour on the lapidary’s wheel—he fully recognises 
the great importance of the exact and quantitative 
methods of the mineralogist. The chapters dealing 
with the scientific methods for identification of precious 
stones are, on the whole, fairly complete and accurate, 
though evidently the information is to a great extent 
second-hand and sometimes wanting in precision. We 
notice that the suggestion of the cz admium borotungs- 
tate as furnishing a dense liquid for the separation of 
Fic. 2.—Diamond Bruting. From * 
gems is ascribed to Prof. Church, and not to W. Klein; 
while the recommendation of the use of the mixed silver 
and thallium nitrates is accompanied by no hint of the 
limitations to the use of this substance imposed by 
its high price and tendency.to change colour. The 
Abbe refractometer is described as a means of deter- 
mining refractive indices, with no suggestion as to 
the existence of simpler and cheaper instruments, like 
those of Prof. Bertrand and Mr. Herbert Smith. The 
use of the Rontgen rays in differenti- 
ating between the various gems and 
paste is described, but no reference is 
made to the valuable and exact observ- 
ations published by Prof. Doelter on 
this subject. In the same way anti- 
quarian subjects, like the classical and 
biblical names applied to gems, are dealt 
with in a very perfunctory manner, the 
uninstructed reader being left in ignor- 
ance as to the wide differences of 
opinion which exist as to the identifi- 
cation of the particular substances re- 
ferred to by ancient authors. 
It is when the author comes to deal 
with the practical work of gem-cutting 
that we feel that he is on safer ground, 
and his account of the method of 
cutting and polishing both diamonds 
and the softer precious stones, fully 
illustrated as it is, has all the complete- 
ness which we might expect from one 
practically engaged in the industry. 
The ordinary methods of ‘‘ solder- 
ing ’’ diamonds into cones of metal 
(consisting of two portions of lead to , 
one of tin), and grinding and polishing F 
facets by pressing them against a 
rapidly revolving wheel armed with diamond dust, 
are well known. Perhaps less familiar to most 
persons is the series of operations—known as 
‘slitting,’’ ‘‘cleaving,’’ and ‘ bruting ’’—by which 
diamonds are made to assume approximately the 
required shape, before the formation of the series 
of facets by means. of the polishing | wheel 
(‘“skeif’’). Diamonds are sometimes: sawn across by 
means of the ordinary lapidary’s wheel, a thin iron 
NO. 1944. VOL. 75) 
The Gem-Cutter’s Craft.” 
iG. 3.—Gem held in position against the wheel. 
dise the edge of which is armed with diamond dust 
but on aecount of the equal hardness of the dust and 
the stone the work is very slow and_ laborious 
Much more frequently the form of the gem. is 
modified by ‘ cleaving,’’ advantage. being skilfully 
taken of the natural octahedral parting-planes ¢{ 
the diamond. The method adopted is that familier 
to mineralogists, and is illustrated in the accom- 
panying diagram, Fig. 1. 
‘“The diamond to be cleaved is 
cemented upon the end of a wooden 
stick or holder in such a position that 
the plane of cleavage to be used in 
the operation lies parallel to the length 
of the stick, which is firmly fixed inte 
the centre of a weight projecting from 
the wooden. bench in front of the 
operator. <A steel blade is held against 
the diamond in the desired position. 
and by means of a smart blow 
upon the back of it, the stone is 
caused to divide along the cleavage 
plane.”’ 
The process called ‘‘ bruting’’ de- 
mands equal delicacy and firmness of 
hand, aided by a_ skill which can 
only be attained by long practice. 
“The bruting of diamonds consists of rubbing two 
diamonds together in such a way that by continual 
friction each can be made to assume the required 
shape. Each diamond is cemented upon the end of 
a stick or holder about a foot long, and the operator 
firmly holds one end of each stick in either hand. 
The stones are then rubbed and pressed one against 
another over a wooden trough containing a very fine 
metal sieve, into which fall the particles of diamond 
From ‘“‘ The Gem-Cutter’s Craft.” 
dust rubbed from the stones. In order to obtain 
sufficient leverage the holders which support the 
diamonds are held against little metal projections on 
either side of the trough ’’ (Fig. 2). 
In reading the work before us the mineralogist 
recognises the fact that a skilled lapidary with powers 
of acute observation may detect phenomena that could 
scarcely reveal themselves in any other circum- 
stances. Among these may be noticed the statement 
