Left is a ordinary dial of Submariner in Gold and Right is with Onyx Dial
There is a thin layer of Onyx seen at the Arrow, the thickness of the Onyx is 0.2mm
and the diameter of the onyx is slightly smaller the inner diameter of the watch perimeter.
This is a ordinary dial, there is no such layer on the edge
There is simple way to tell that the dial is ordinary painting dial of Onyx
1. there is a Gold Trim insert at the Date window of the Onyx dial.
2. There is a thin layer seen at the rim of the Onyx dial, it is very obvious under a 10X eyepiece.
I used my Handphone to capture the detail as shown on top.