Hard Enamel can be utilized on all coins when 2D surfaces are used.
3D coins must use epoxy as a protectant for painted areas.

Shiny metal finishes can have a stoning process done on the coin, which creates
flat paint. Antique metal finishes does not allow for the stoning process.|
Hard Enamel or Epola replaced the traditional Cloisonné style.

Here is an example of Cloisonné. Hard enamel replicates this look.

Hard Enamel example