The Permaset range of eco-friendly water based inks contains some metallic inks. Different from foiling, the inks themselves contain glitter particles, which lay down with the ink. These larger particles do not easily pass through the mesh of fine screen printing screens, especially with the silver and bronze inks, so very high detail may be difficult to achieve. Prints cost only 20% more than a standard print and the effects are stunning.
It's also worth looking at their pearlescent range of inks too - these also have a metallic effect but more of a matt finish, a bit like a shiny pearl.