How do I radial gradient shade an open object? Not a plane or a sphere.
Like the attached blend file.
Either, for example, white at both ends, black in the middle or black at both ends, white in the middle.
A gradual gradient from one to the other side, linear from left to right, up, down, doesn't matter, or from the outside of the object in, or the inside of the object out. Saving it as an image wouldn't accomplish the same objective.
When I try, Radial doesn't seem to do it.  Neither does quadratic sphere. Nor gradient texture.
Most of what I've seen applies to closed objects like spheres, or flat, or flat surfaces, like planes.
A simple gradient texture would do this. Use a gradient texture (I used spherical) with object texture coordinates (add the object you want the coordinates to come from in the Texture Coordinate node), and a *Color Ramp (Ease interpolation* would probably give the best result) to adjust the contrast as a mask between two shaders as shown below:

Click to enlarge
Also, it is important to apply scale to see correct results.

This should give you a result like this:

Here is the modified file: