Hello!
The latest fashion for jewelry is to add color to metals. It can be done by understanding their reactivity. For example, the oxidation of reactive metals (Nickel, Aluminum, Niobium, Titanium) on top of unreactive ones (Gold, Silver, Platinum), results in the formation of oxide layers that serve as decoration for jewelry.
So, understanding reactivity is helpful for making jewelry because it helps to know which metals can be used for decoration and which ones can be used as support for the decoration.