Does curvature "affect" luster, or the perception of?

[Raisondetre]

I'm just wondering because I'm wearing this random button freshwater pearl ring which has pretty good luster, and compared to a high-grade full strand that's round and of the same size, it "appears" to have better luster with a clearer "mirror" effect. It got me wondering if it's the flattened surface. On a perfect sphere the reflected light is more diffused due to the ever changing curvature. Anyone care to confirm this?

[Valeria101]

Isn't a 'button' somewhat like a sphere with a flattened side? I would imagine that the dome part is very close to a section of a sphere. No idea why that might make any difference for the 'nacre optics' compared to a section from a full sphere.

Or is the pearl flater then that ?

Picture Source


What comes to mind, is that... roundness is quite a big deal for pearl grading. And, unlike lustre, it is measurable, which makes it even more commercially important. More then lustre... in the real world... so maybe the grading system applied to your pearls allowed some tradeoff in response to the lowest common denominator of demand . Can't know what that particulat in-store system was and how it is applied

The ripply surface of baroque and circlee pearls is supposed to enhance orient, and the 'fish eye' effect on dark round pears depends on shape and depth of nacre... but, I've never heard of any other relation between pearl shape and its optic properties. Not until now, that is.

[Slraep]

Hi Raisondetre,

There is a difference in perception of reflected, refracted and defracted light hitting a flat nacreous surface like MOP versus a curved nacreous surface like a pearl. On a curved surface, the edges of the thin layers of seemingly poured nacre(the edges of cabbage leaves around a head of cabbage), are more exposed to light, and something magical happens on those exposed jaggedy edges of crystalline aragonite that doesn't with flat MOP. Normally, a curved surface should have more lustre, but this isn't always the case. There are many other factors that determine lustre too.

Slraep