@Astrotitan
I mix my paints with a flow agent, which makes normally matte paints fairly shiny, even when they aren\'t normally.
In those situations, I use a matte coat (dullcote) to remove the unnatural shine, then go back with a *very* watered down gloss varnish over metallics, gems, etc. that I want shiny. It fills in over the rough (matte) surfaces, and restores the luster.
I also find that if you shade the metallics a lot, the dullcote actually enhances the shading, so I sometimes skipp the gloss step if this is the case.