What lighting and background will make a realistic gemstone?

Question

The gemstone material is GlassBSDF (RGB (1, 1, 1) and Alpha 0). The Background is a Gradient Texture and Radial.

As can be seen from the rendering the gemstone picks up Gradient colors but it does has distinct facets.

I tried a HDRI but the gemstone picked up colors from the sky and ground.

I tried all the lamps and emitting planes but could not get distinct facets.

Since the gemstone is symmetrical about the X and Y axes the rendering should also be symmetrical.

If the camera is more than 100 units from the gemstone only the background is rendered.

When an animation is made by rotating the gemstone there should be flashes of total reflections from facets but there are none.

I need help with lighting and background to achieve a realistic gemstone with distinct facets on a White background and total reflections from facets.

Any suggestions would be greatly appreciated.

Thanks

Of all the Blender renderings of gemstones that I have seen I have yet to see a realistic gemstone. Gemstones have three general areas. The Crown, Girdle and Pavilion. The Crown usually has a flat on top called the table. Some crowns come to a point called an Apex Crown. The girdle can be faceted or a smooth surface. Round Diamonds have a smooth cylinder for the girdle. Ovals have a smooth ellipse girdle. Some rectangular cuts have rounded corners which are portions of smooth cylinders. The pavilion may come to a point called the culet. Cuts that are longer than the width sometimes have a line for the culet or called the keel. Gemstones can be composed of planes, cylinders, cones and spheres. They are not restricted to only planes. The intersections of facets are sharp regardless of material. Do not round edges!

I have seen Blender rendered gems that the crown and pavilion touch each other with a sharp edge (No Girdle). When these gems are mounted there is a good chance that they would be chipped when forming the prongs. This is why gems have a girdle.

I have seen Blender renderings of Diamonds with diamond shaped crown mains. The crown mains of Round Diamonds are kite shaped.

Faking dispersion and other enhancements looks faked. If you want good dispersion then Spectral Rendering is the answer.

The gem should be transparent not translucent like Rose Quartz.

I know what a gemstone should look like because I have been cutting and designing gemstones for over 65 years. I know how light travels through gemstones, I’ve done the math.

I use the gemstone rendering as a tool by reading each pixel and computing a brilliance value. The gem is rendered with different angles, different camera positions and the brilliance value calculated. The angles are changed using the Ratio of Tangents formula thereby not changing the Crown and Pavilion view. From this data cutting angles can be determined for the brilliance desired.

So far my question has not been addressed.

Focus on the Gradient Background. The gemstone in the screen shot has excellent transparency, distinct facets and the animations are great. The problem is the Black area in the lower left corner. The gemstone picks up this Black color and is no longer symmetrical. I want a background with the properties of the Gradient Background without the Black gradient coloring.

Answer 1

Lighting gems is an art that requires lots of patience, and what works for some scenes might not work for others.

With glass objects you are dealing mostly with objects that do not require to be lit, but do require other objects to be reflected on their surfaces, or seen trough them. In other words glass and crystals main attributes are that their surfaces are reflective, transparent and refractive.

So you need to create an environment that is conducive to show all of this characteristics.

Choose a background that will make your object stand out.

Create nice reflections:

Make an environment that is not homogeneous (like a flat color), but that has variations, for example a voronoi texture like in this setup:

Or create a World that has some texture but that is not necessarily visible to the camera.

To show the transparency, place an object behind the glass (you can choose to make it invisible to the camera by turning off ray visibility)

To add more accents add other emissive plane objects with different sizes and shapes and intensities, and place them so that they can be reflected on the faces of the crystal at certain angles.

Rotating the object will make those objects reflect differently:

After that you can add post-production effects on the compositor, like glares, streaks etc.

All of this examples were done using the default glass shader and no lights.

Answer 2

It's evident that you have a deep understanding and passion for gemstone rendering, and your attention to detail is impressive. Achieving a realistic gemstone with distinct facets and accurate reflections is indeed a challenging task in Blender.

Regarding the issue with the Gradient Background causing the gemstone to pick up the black color from the lower left corner, one possible solution could be to create a custom background that mimics the properties of the Gradient Background without including the black gradient coloring. You can experiment with different background textures or HDRI images that have the desired color and lighting properties for your gemstone. Adjusting the lighting setup and camera angles might also help in achieving the symmetrical rendering you desire.

Additionally, using spectral rendering for dispersion effects can lead to more accurate and realistic results, as you mentioned. It may require a more complex setup, but it could be worth exploring for achieving the level of realism you're aiming for.

Keep experimenting and refining your rendering settings, and don't hesitate to seek help from Blender communities or forums. With your expertise and dedication, I have no doubt that you'll be able to create stunning and lifelike gemstone renderings.