Adding a metallic finish as opposed to a solid gray or silver tone is a very simple and easy process that will dramatically improve the caliber of your cake.
Mix in silver luster dust with a clear piping gel until the mixture gains a smooth consistency. Put the mixture in a piping bag. Apply the silver gel as you would to normally decorate the cake.
Now that you have applied the silver piping gel, add some pearl luster dust to your air brush extract, creating a nice metallic color. Lightly apply this mixture to your entire decorated cake, resulting in a beautiful metallic finish. If you would like to learn more, watchthis helpful demonstration.