The refraction index is an optic characteristic among others of glasses. It depends on the sample’s material as well as on the wave length of the utilized illumination. The refraction index in case of measuring with a wave length of 589 nm is denoted as nD.
For measuring of massive samples serves for example an Abbe refractometer.
After embedding in a suitable possible immersion liquid the measurement of granulates is possible.
(Samples: plane parallel sheet, polished one-sidedly, 20 x 20 mm or an appropriate blank respectively granulates, circa 20 g)