This was rather a fun figure, though interestingly I think he was sculpted a bit on the short side by modern standards; he stands noticeably shorter than Strahd does from the same set, whereas according to the current descriptions Harkon's got over half a foot of height on the vampire (6'8" vs. 6'1, according to Gazetteer I). It's a well-detailed figure though-- so much so that I took the time to include a back view showing the harp he carries.
The two main notes on his paintjob are the monocle and the coat. To give the effect of reflectiveness in the monocle's glass, I used a stuff called Pearl Luster Medium, by Delta Ceramcoat. It's not a metallic exactly, as it's white rather than silvery, but it is a suspension of fine shiny particles (mica, maybe?) in a clear acrylic medium which can be mixed with other colors to give them an interesting sheen. I also use it for the monocle of the doctor in the Village Personalities set, and experimented with mixing it into colored paints for Tristessa, about which read more here.
For Harkon's coat, I decided to take the description of it as gold quite literally-- which created some interesting problems. Most of the time, metallics are applied to armor or swords, or used to pick out jewelry. Shading them can either be by the simple use of black (in textured armor like chainmail) or even by leaving them unshaded (for flat surfaces like plate armor or blades, or for very tiny things like jewelry). The coat, however, has contours that call for shading... and shading metallic gold is not as easy as I thought. I ended up using orange ink (some have also used red-brown inks like Citadel's Flesh Wash) to decent effect, and if I had known about the technique of mixing a pure, light silver into other metallics to lighten them (much as when you mix white into non-metallic colors), I would probably have used a touch of a silver-gold mixture to pick out highlights on the coat.