You chose silver and black for the ghost flames, you really didn't mention what color you are doing the flames on so I don't know if this will give you the "ghost" effect or not. Usually silver covers pretty quick (versus, let's say a white pearl). So the more silver you put on, the less the ghost effect appears. You may want to really thin down your silver, just to make sure it doesn't cover your base too quick. Keep checking each coat (by pulling up a small piece of tape next to the base in an inconspicuous place) just to make sure you get the effect you want.
If you want your skull to stand out slightly, I would suggest making the color a little lighter then the area in which you are spraying in the flames. You might want to highlight the skull in shades of a light gray.
Be sure and post some pics when your done!
