What is a shimmer ink?

Shimmer inks, such as the Diamine Shimmertastic series or Herbin 1670 inks, sparkle as you write. They do this because there are micro particles suspended in the ink that reflect either silver or gold, depending upon the colour. They're fun for writing letters and cards as they add a unique character to your writing. Shimmering inks are perfectly safe to use in fountain pens but sometimes it can take a while to completely flush out the particles if you want to go back to conventional ink.