A mid-toned blue-black, Salix (and it's sibling Scabiosa) is a popular Iron-Gall ink. It's milder (with lower IG content) than traditional formulations, but care should still be taken to use frequently, never let it dry in the pen, and clean the pen periodically. The blue component of the ink will wash away, but the IG part is water resistant.
by Prolix