What works for me:

1. I use at least 2 sources of constant on light, not flash. A main light and a fill.
Best position is from the sides and slightly high, not from the same direction as the camera.
2. Do not use too much light and burn highlight. It's better to use long exposure & tripod.
3. I look into live view and adjust items position. Use something to hold it in place or adjust light position to get the best sparkle.
4. I use a dedicated macro lens or a long lens (at least 140mm). This creates a flat image and predictable reflection/sparkle from the item.
5. Single point focus
6. Stacking focus to get more depth
7. Take as sharp as possible image. Sharpness & contrast creates the best sparkle.
8. Edit the photo. Get the best photo possible but also edit afterwards to make it pop even more.

Things to consider.
1. Clean the items before taking photo. Make it look its best. Is hard to edit dust & fingerprints out.
2. Be careful of reflections. Oftentimes you will see yourself or stuffs around you in the item and may need to be edited out.
3. The color of light and the background the the item is resting on will affect the reflections. A colored background may be used to enhance the stone, then edited out. Replace with black background.
4. Sharpness & Contrast does a lot to make a jewelry look awesome. Try to find the right balance of this in taking the picture and in editing.
5. If using a lightbox, try having one of the panels (the base or the back wall or front wall) provide some contrast.
6. Use Low ISO. Base ISO if possible.


Hope this helps.

Somewhat of a contrarian view here. I inherited a very large sparkly diamond. 5 ct. it was beautiful. I happen to have a friend in the diamond business. Took it to him and he immediately saw flaws (which I also saw using a loop) and suggested we cut the diamond down to enhance value. So a 3ct diamond was going to be worth more than a 5ct? In a word, “yes.” Also said to have it graded by the gemologist, get certificates ,etc. Bottom line, photos don’t mean much. It is the grading on clarity, size, and cut that will sell a diamond. I would rely on a diamond expert and skip the photographs.

Somewhat of a contrarian view here. I inherited a very large sparkly diamond. 5 ct. it was beautiful. I happen to have a friend in the diamond business. Took it to him and he immediately saw flaws (which I also saw using a loop) and suggested we cut the diamond down to enhance value. So a 3ct diamond was going to be worth more than a 5ct? In a word, “yes.” Also said to have it graded by the gemologist, get certificates ,etc. Bottom line, photos don’t mean much. It is the grading on clarity, size, and cut that will sell a diamond. I would rely on a diamond expert and skip the photographs.

Still... and I posted on this thread about getting a good professional appraisal. As another respondent said, the OP was looking for photo advice and most of us, myself included, failed to give the requested advice. For myself, sorry for that. As legit as all the appraisal advice may be, it does not help you take superior photos of your diamonds. So, the two light method is a good start. While one might be tempted to use a light tent or another form of diffused light, another light providing sharp specular light is more apt to giving the diamonds the sparkle you seek.