I created another pattern,and used the chemical symbols, gold and silver.

copy layer and chaged to gradation color of central circle.

 change to overlay only central circle.

As a result, it becomes visible  the boundary line.

I thought the overlaid the two forms, not gradation processing is much better results.

This gradation effect I think that good results.

When I joined a"Steampunk"class, I wanted to create  like this design and use 3D technique.

this time ,for the first time to learn how to use the 3D, it was very fun!

Thank you Helen!