How many directions should you check for doubling?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (C)

Doubling shows up as a second image or offset of a facet or edge, and that effect can be visible only from certain viewing angles. Because its appearance depends on direction, you need to inspect the stone from multiple orientations. The reliable approach is to view along three mutually perpendicular directions—the three principal axes of a cube-like crystal. In practice, rotate the stone and compare what you see across views that run along the table-to-pavilion axis, across the girdle, and in a diagonal orientation. Checking these three directions covers the main orientations where doubling may appear, so you’re less likely to miss it. Looking from only one or two directions can miss doubling that shows up only in another angle, while four directions isn’t necessary once you’ve covered the primary axes.