The transparency of the diamond can be understood as transparency of
If we fill a glass of water from pristine mountain stream and
compare it side by side with the glass of water from the tap, the
difference can be seen.
The will be on other material visible but 2 glasses will look
In diamond it can be explained by how well the crystalline structure
was formed. We know that diamond crystallizes in the cubic system,
but in process of formation there could be slight defects in the
crystalline structure. These defects, not visible even under
relatively high magnification, will interfere this the passage of
light and render diamonds less transparent to a different degree in
different diamonds. If diamond comes from geological deposit which
formed slowly the crystal structure would be more approaching ideal
and therefore more transparent to light. Golconda mines were such a
slow formed geological deposit. It is not likely that one can
encounter Golconda diamond, but to judge "water" in general,
submerge diamonds in liquid with refractive index approaching
diamond's and compare the degree of visibility. The one less visible
will be the one with higher transparency. Even distilled water can be
used, but of course with less accuracy.
There is a book. The title is Romance of The Golconda Diamonds or
something similar. I even think I saw it on GIA website bookstore. It
should provide more on the subject.