140 PREPARATION AND MOUNTING 



&c., are of no avail. Most of these require no particular 

 care in mounting, but are placed in balsam like the other 

 objects noticed in Chapter IV. : where, however, any special 

 treatment is necessary it will be commented upon as we 

 proceed. 



SHELLS, &c. It is seldom, if ever, necessary to possess 

 apparatus for this process except a small thin saw made 

 with a steel blade, for which a piece of watch-spring serves 

 very well ; a fine stone such as is used for sharpening pen- 

 knives ; and two smooth leather strops, one of which is to 

 be used with putty-powder to polish the section after grind- 

 ing, and the other dry, to give the final surface. It is, how- 

 ever, very convenient to have three or four files of different 

 degrees of fineness. A very useful implement in this process 

 is the Corundum file or rubber, sold by most dealers in 

 watchmakers' tools. It may be procured of almost any size 

 or grain, either circular or flat, and will cut almost any- 

 thing. They possess the very great advantage of not carry- 

 ing much, if any, impurity into the texture of the object 

 upon which they are used. The shell, if very thick, may be 

 divided by using the watch-spring saw; and this section 

 may then with ordinary care be rubbed down with water on 

 the stone until one side of it is perfectly flat. When this is 

 accomplished it must be rubbed with putty powder upon 

 the strop, and finally upon the other strop without the 

 powder. This surface will then be finished, and must be 

 firmly united to the slide in the position it is intended to 

 occupy. To do this a small quantity of Canada balsam may 

 be dropped upon the middle of the slide and heated over 

 the lamp until on cooling it becomes hard ; but this must 

 be stopped before it is rendered brittle. Upon this the 

 polished surface must be laid, and sufficient heat applied to 

 allow the object to foil closely upon the slide, when slight 

 pressure may be used to force aside all bubbles, &c. On 

 cooling, the adherence will be complete enough to allow the 

 same grinding and polishing upon the upper surface which 

 the lower received. Whilst undergoing this, the section 



