The subject of scintillation is a bit more complex as it generally involves how much "pop" we see in any given diamond as well as an examination of "patterning" that takes place as we observe the diamond in diffuse lighting.
Scintillation itself can be observed in any lighting environment but will differ in nature depending on whether the diamond is viewed in diffuse lighting or spot lighting.So while we're talking about diamond appearance in diffuse lighting and before you watch some videos on the subject now is a good time to introduce you to what GIA refers to as "Patterned Scintillation" and what AGS simply refers to "Contrast".
The pattern and contrast to be observed in diffuse lighting is that of both bright and dark reflections observed within diamond. To use a very simple analogy lets say we start with a flat white piece of paper.By itself it has no pattern. No contrast whatsoever.When we add dark reflections along with the bright reflections it will form either a pleasing pattern to the human eye or it will not. In optical sciences, when there is a balanced distribution of dark reflections mingled with the bright reflections it forms a more pleasing pattern to the eyes and can in fact make the object "pop" so to speak.This would be referred to as "positive contrast".
No contrast whatsoever.
Poor contrast due to displeasing patterning.
Positive contrast due to good distribution of bright/dark reflections.
The same truth holds with diamonds as well.The "pattern" can be observed while the diamond is in a static position but is more interesting to observe while it is dynamically moving.
Here are examples of static patterned scintillation in a variety of round brilliant cuts.