By metallic ornaments, I mean the ornaments that's part of the helmet on the far left side of the picture. What do you call them?
Since I am not aware of any word used solely for this purpose, I'd use one of the following words, depending on the context whether you want to describe a single element or a set of them:
- As you have named them, the ornaments is a good generic label of decorative elements of art. They might follow a pattern.
- A motif is a common word used in art and iconography as well.
- A pattern represents a regular and repetitive arrangement of elements. It might be suitable for most of the armor pieces such as a chain vest is.
- A decoration is yet another general description of ornaments. This is either used in a lot of museums (see Metropolitan Museum of Art) as well as embellishment.