Reflectance measurements were made in accordance with AS 2486 using a Leitz MPV 1.1 photometer mounted on a Leitz Orthoplan microscope. The objective used for reflectance measurements was a 50x NPL oil-immersion lens. Synthetic spinel (R = 0.416%) and garnets (R = 0.817% and 1.76%) were used to calibrate the photometer. The low reflectances of most samples meant that the spinel was generally the primary standard used.
Each reflectance measurement reported is the average of two measurements of the maximum reflectance for the field (back-projected area of the spot size in the field of view on the sample is a rectangle approximately 0.001 mm x 0.002 mm), the two measurements being separated by rotation of the stage by 180°. Stage rotation gives a measure of the local flatness of the polished surface. A minimum of 25 fields were measured on every sample where sufficient vitrinite was present. Where 25 fields were measured, the mean quoted is effectively the average of 50 measurements of vitrinite reflectance.