It is a cobalt or nickel like metal plate. The surface has been hammered, so it is very uneven and bumpy. The surface is also oxidized affecting the reflection.

Recently, hammered copper artworks become very hot in the world. Hammered products includes cups, plates, bowls etc.

To create this hammered pattern, complex 3D modelling is NOT required. This texture is designed to be directly used as a skin. Then the model will have this fashionable hammered effect.