Higgins Eternal is a very good calligraphy ink. Whether you are an advanced calligrapher or a beginner: this is a must-have black ink. The ink dries matte with a very small gradient but is largely opaque. The ink is not waterproof.
As the name suggests, the Higgins Eternal is an Archival ink: it is very lightfast!
You cannot mix the ink with other inks, but you can dilute the ink with a little bit of water.