Keith Newton
A diffused source seems to kill it. It shows best, when you have a strong polarized light source from a great distance, like the Sun.

Then it works best, when the reflective angle from that source is from the side, rather than down the grain, so don't have the axis of the pen pointed toward it.

Then, I think the term is angle of incidence, which is like when a pool ball, without spin, strikes the rails, it bounces off at more or less the same angle.

It seems like the Sun would make a perfect place to shoot for this, and it might be, if there wasn't so much blue ambient light coming from the Tyndall effect making the blue sky. This is why, if you have ever gone to the Grand Canyon, when you stand and relish the red rocks, then when you get home to view your photos, the rocks show up as gray brown, rather than how you brain remembered it. The longer wave length of warmer light seems to help enhance it.