By Jim Perkins (with Bruce Harding)
Copyright 2010
I am often asked how to choose good angles for faceting. Some of the answers were published in 19751 and are now available on the Internet at the address provided in the footnote. One subject is ‘windowing’, which means that light passes directly through the gem without internal reflections; generally when the table is tilted from ‘normal’ (perpendicular) to a line from the viewer’s eye.
This was discussed in the subject article2, which provides charts for common materials. Each of these lists pavilion slopes across the bottom, and the maximum angle of tilt without windowing is listed across the top. Since nothing else matters in the subject of windowing, these data can be listed simply as below:
Note that quartz with 43° pavilion mains...
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