Without an idea of scale its hard to say if its is actually decoration. It looks like a well corroded part that has been cleaned and made shiny.
The nut seems a combination of processes. Has a tap been put through it after the surface was 'decorated'?
I cannot imagine what sort of product would benefit from this so called decoration, it does not look very engineering like are pretty in any sense of the word (but I know beauty is in the eye of the beholder)
Ian P