There is a kind of jade similar to omphacite, with special attributes characterized by blackness in the reflecting light, greenness in the transmitted light . Now we need to establish a color grading standard but common color evaluation is based on reflected light, so What should we pay attention to if we want to evaluate color under transmitted light?
Clearly the task is to characterise the observed green light which will have a specific spectral power distribution (SPD). If you your specimen may be set up in the cell of a transmission mode spectrophotometer a full spectral SPD could be measured and characterised in terms of its CIE Standard Observer Tristimulus co-ordinates. If no such instrumentation is available I suggest you allow the transmitted light to fall on white paper and compare the resulting colour patch with the visual colour chips of a colour order system such as Munsell the International Color Council (ICC) or Chromashare.
For colors of gemstones which turn obvious under transmitted light, it’s more efficient to spot them by using the method of transmitted light test. This method works by adding a bottom light source to be testified and requires guarantee of polishing and smoothness of gems. Additionally it sets certain influence on the result that the thickness varies a lot from each other. Under the transmitted light we can evaluate the colors of gems based on the uniform color space CIE 1976L∗a∗ b∗ for three parameters, say lightness, chroma and color hue.
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