The challenge with this Jewelry is the Balance of Hard Light vs. Soft Light.
The biggest Section of this Necklace is a high polished, glossy Part. Also the Shape is rounded. To make this visible on a Photo you will have to create a Gradient to make the rounded Form visible, and a Highlight to show that it is a glossy Material.
The tricky Part are the Gemstones. Gemstones generally need diffused Light, but not too soft, otherwise the Facettes won’t be visible. That means the Lightsource should be very close to the Diffuser.
Lightsource close to a Diffuser is not working very well, when a Gradient is needed for the round Part of the Necklace. So, the only Solution is to work with a Cone, which covers the hole Jewelry. The Lightsource for the Gemstones needs a Modifier to create a tiny Spotlight, also the Lightsource which creates a Highlight on the glossy Part of the Necklace.
The third Light which is used to create the Gradient needs a Reflector with a Honeycomb Grid to focus the Light and create a smooth Gradient on the Cone, that will be reflected on the rounded Part of the Necklace.
I didn’t want to work with Focus Stacking to get the whole Necklace in Focus, I preferred to use a shallow Depth of Field, makes it even more interesting in my Opinion.
