The effect is easy to observe on a smooth, flat-black material(e.g. poster-painted paper), but you can see it on a fingernail or a worn coin as well.

• 在一个光滑的、平而黑的材料上（例如招贴画的纸）容易看到这个效应，但是也可以在指甲上或旧的硬币上看到。