FAULTS 91 



considerable difficulty in obtaining naturally coloured stones of exactly the same shade of 

 colour. This difficulty may be overcome by coating the back of a dark stone with a light 

 pigment or a pale stone with a darker pigment, and thus securing a uniform depth of 

 colour. 



A very effective artifice is that of placing beneath a stone a second of the same form 

 of cutting. Large rosettes are frequently treated in this way, a smaller stone and a foil 

 being placed under the rosette in the closed metal case in which it is set ; by this device the 

 brilliancy and lustre of the rosette are wonderfully increased. Similar manipulations will 

 be fui-ther considered when we come to treat of the imitation of precious stones. 



The use of these and similar artifices for increasing the beauty of a stone is naturally 

 attended with less difficulty when the stone is mounted in a closed setting and one side of it 

 entirely hidden from view, than when an open setting is used. Even in the latter case, 

 however, such artifices may be made use of to a certain extent ; thus, a thin strip of foil, or 

 a coating of pigment is applied to the inner side of the setting just below the girdle of the 

 stone ; this often has the effect of increasing the brilliancy and colour of the stone. A ruby 

 of too pale a tint mounted in an open setting may be treated in this way, the inner rim of 

 the setting being coated with carmine-red enamel, which gives the stone a very beautiful 

 depth of colour. Other precious stones are treated in corresponding ways. 



H. PAITLTS IN PRECIOUS STONES. 



The beauty and value of a precious stone naturally depend on the absence of all 

 disfiguring faults within its substance or upon its surface. Thus a perfect specimen of a 

 gem must be free from cracks and fissures in its interior and its lustre and polish must be 

 uniform and uninterrupted over the whole surface. A transparent stone should be perfectly 

 clear, with no cloudy patches, and free from all enclosures, especially of small, opaque, 

 foreign substances. Colourless stones ought to be quite free from any faintly coloured 

 patches ; while the colour of coloured stones inust be uniform and regularly distributed, 

 so that the stone shows no light or dark patches, or differently coloured portions of its 

 substance. Exception to the latter rule is, of course, made in such a stone as agate, the effect 

 of which depends on a difference of colour in different portions of its substance. Each 

 imperfection of the kinds just noted, each crack, each dark or cloudy or differently coloured 

 patch, is a fault in the stone, and as such detracts from its beauty. It is in transparent 

 stones that faults are especially noticeable, and in a cut form they are reflected again and 

 again from the facets and thus rendered still more obvious. 



Small insignificant faults, when they are few in number, do not render a stone entirely 

 unsuitable for decorative purposes, but they do diminish its value, and that sometimes very 

 considerably. When, however, the appearance of a stone is so disfigured by the presence of 

 numerous glaring faults that its use for ornamental purposes is out of the question, it 

 becomes absolutely worthless, unless indeed its hardness enables it to serve some useful 

 technical purpose. 



The more obvious faults of precious stones, such for example as the presence of light, 

 or dark, or differently coloured patches, are easily detected ; they are indeed often apparent 

 at the first glance. Frequently, however, the detection of faults requires a practised eye, 

 since a clever gem-cutter will so arrange the facets of a stone that any faults it may have 

 become quite inconspicuous and almost unnoticeable to an unskilled observer. When 

 considering the subject of the refraction of light it was mentioned that the faults of trans- 

 parent stones may be made more conspicuous by immersing the stone in a strongly refracting 

 liquid, such as methylene iodide or monobromonaphthalene. This device is due to Sir 



