الوصف

 1.The steps as belows:

â‘     Chose a polished plane(make it clean) of the gemstones,make the gemprolate axis parallel with test table,then drop some liquid on the test table.

â‘¡    Observe theshadow edge through the ocular.Generally,you can see the two shadow edge very very close.Use the polarizing filterstrengh the observing effect.put polarizing filter the on the ocular,and revolve it,until one of the shadow disappeared,the other shadow edge is very clear,write down the scale valueï¼›then revolve the polaroid sheet again,make the disppeared edge turn up ,the recorded edge dispeared,write down the new scale value.So do as above,you can get two refactive index value.

â‘¢    Every time revolve the gem stones of the angle *5°,repeat the step②，you can get two refractive index value at every place,till you get 4 pairs of data;

â‘£    Chose the min and max data,and the margin between them,they are the mininum refractive index,the maxinum refractive index,and the maxinum double refractive index(birefringence).

2. Additional remarks

â‘ If the gemstone you test is monorefringent,you can only see one shadow egde at every place.but you will get different scale value because of theplaneness of plain.so different place may get different scale value,they not the birefringence.

â‘¡For the birefringent genstones only have one refractive index at some direction,so you should test two different place to make sure whether it is monorefringent

â‘¢Use the refractometer can easily know whether the gemstone is double refraction or not,revolve thepolarizing filter quickly,if the shodaw edge bobbing,it is thebirefringentgemstones.

Use the step of getting the maxinum R.I. you can also know whether the gem stone isuniaxial crystal or biaxial crystal and also can know the it’soptic sign.Please consult the relevant books.

II:Ways of testing the cambered surface and skill facet gemstones

1.      For those gemstones,you can only use thepoint measurem to getapproximate R.I

Steps as belows:

â‘     Take off the polarizing filter from the ocular;

â‘¡    Chose a suitable place of the gemstone and keep it clean;

â‘¢    Carefully extrude a little oil on the test prism,make the test place of gemstone in contact with the liquid;

â‘£    Keep your eyes far from the ocular(****0CM),observe theformation of image.the image is related to the shape of gemstone; For the cambered surface gemstone,the image is round or oval;small facet shape for skill facet gemstones

⑤    When you see the image,make your eyes up and down,you will see the image is move with your eyes,and pay attention to the color change in this course;generally,the imageupwardgauge is dark (near the mininum scale),and become bright when move to the maninum scale

â‘¥    When the image move to a place,half bright and half dark,the edge of the gauge is theapproximate R.I.

⑦    Test result have something to do with the liquid.when the liquid is too much,will make the edge black,you can hardly see thephenomenon.of harf black and harf bright.at this time ,you must take off the gemstone,clean dry theliquid on test table,then put on the gem again;if theliquid also too much,repeat the step again,till the edge not with black edge