I think Waterman's "Florida Blue" is one of the best blue inks ever made. It is
a consistently excellent, safe, smooth-flowing deep blue. As the ink level drops
in the bottle, it can be tilted to rest on the angled side so it's still easy to
fill most fountain pens.
I bought this ink after reading how much people love it on the fountain pen
network and I am so glad that I did. It is a lovely blue ink. I love how it
looks when it is dry. And because it is a reasonable price you can spend all
day writing with it and not feel guilty about using it.
Beautiful color, affordable and flows nicely. This is now my default go-to ink.
(of my ~20 inks!) My friends in the SF fountain pen posse say that this ink is
reliable in their vintage pens and they use it to help flush other ink residue
from their sacs.