Quote - Acadia,

Is there anything in the image for the diamonds to reflect?

As for Material vs Material collection - If you were going to save this set up for this jewelry, both metal bits and diamonds you'd save as a material collection. It would probably not work in another piece of jewelry unless the material names were the same. Collections are good for character texture set ups.

It's an image of a bride wearing a tiara. Nothing else in the scene, just her.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi