MANIPULATION. 261 



handle to the ruler be preserved throughout, else in parts the 

 glass wiU be cut, and in others only scratched. A true cut will 

 be known by being very faintly visible, and by a particularly 

 musical sound being produced by the cutting, whereas a scratch 

 is known by its jagged edges, and by the rough and harsh sound 

 made whilst the diamond is passing : when the glass is held 

 towards the light, it will be seen that the scratch is merely 

 superficial, but the true cut, although faintly seen on the 

 surface, will show that the glass is cracked for some con- 

 siderable distance below it. When we try to separate the 

 slip which has been cut with the diamond, we shall find that 

 it easily breaks off, whilst the scratched portion wiU be with 

 difficulty, if at all, removed. The operation of cutting, 

 I although at first sight very simple, will be found not 

 to be so in practice. The best plan for the tyro is to 

 procure a piece of soft glass, and make a number of 

 cuts as near to each other as possible, and try how 

 thin a slip can be broken off. 



Writing Diamond. — The writing diamond is repre- 

 sented by fig. 169; it is not provided with a swivel, 

 neither is the handle squared, but consists for the most 

 part of a thin, tapering stem of ebony or ivory, and as 

 it, like the glazier'rdiamond, will only cut or scratch in 

 certain positions, it is requisite that the operator should 

 ascertain this point, and when once found, a mark 

 should be made on the handle, in order to show which 

 part of it is to be held in front. Those diamonds 

 having a portion of the handle squared on which to 

 place the thumb or forefinger will be found to be by far 

 the most convenient ; but when the operator has once 

 fixed upon the best writing point of the diamond, he 

 pi- jgg may, if he chooses, cut out a place in the handle for 

 the reception of the thumb or forefinger. There are 

 two descriptions of writing diamonds, one in which an irregu- 

 lar stone has been ground or turned to a fine point, whilst the 

 other is formed of a sharp-pointed fragment or splinter. The 

 former is to be preferred, although its cost is considerably 

 greater. 



