You would use a glossy varnish to seal it. There are many different kinds, some are better than others. They're pricey, though, since they are made for cars, but they are built to last and withstand the weather. The best kind are the ones you put into a spray gun, though, but that's a lot of extra work. Your best bet is to head to a home depot or Lowes or a similar place to find a good gloss coat (if you want it shiny) as a spray paint and practice spraying something to prevent drips. Or the automotive one that is the real deal which you can get at car places, but they are about double the cost.
Edited by Midorime, 26 August 2014 - 09:14 PM.