Non-metallic metal (NMM) painting is the technique of using regular paint (without metallic content) to give the illusion of a metallic, reflective surface. In general, NMM requires high contrast painted with smooth transitions from light-to-dark.
There is also the need to understand how light interacts with reflective surfaces and within the context of the surrounding environment.
In short, NMM is an advanced painting technique for miniature painters. I felt it best to make a video of how I paint miniature swords using NMM. There are a number of other sites with great tutorials. I tend to borrow a number of techniques and mix them all together whenever I feel it fits the need.
In this case, however, I have found that the loaded brush blending approach is the quickest for small surfaces that are flat.