How was the star design formed on Captain America's shield?

Question

In Captain America: The First Avenger, we see that the shield (in unpainted vibranium) was manufactured with concentric rings that line up with the red and white stripes, but no sign of the central star.

But in later appearances, we can see that the outline of the white star, along with a less prominent inner outline and five radial lines within the star, is embossed or engraved into the shield as well.

Was his shield remanufactured at some point with these new features? Was this before or after he was frozen? In the best image of the shield that I could clearly identify as being from TFA, it wasn't clear whether the lines were present (it's a bit blurry - if they're present at all they seem less prominent than the concentric rings):

Answer 1

The very simplest answer is that vibranium isn't adamantium. Although we don't personally see it being moulded and shaped, we do see it in its raw form being turned into all sorts of useful items like Cap's shield and Ultron's body armour. Vibranium may be heavily resistant to impacts, but it isn't impervious. It can be cut, shaped, melted and remade to the user's needs. It can even be scratched by hard enough impacts.

Steve chose it, Stark Sr. (modelling it on Captain America's existing shield) painted it for him and engraved a star onto it.

Answer 2

the most logical explanation is that the shield was covered with some other metal like aluminium or iron to be able to paint or for some other reason like adding straps. we see the shield scattered multiple times but it's as good as new at the beggining of every movie. it would also explain how the shield, wich is "completely vibration absorbent" gains the ability to redirect attacks or bounce off surfaces. as ultron said: "the most versatile substance on the planet"