Denneweg Green ink made by P.W. Akkerman pen store in The Hague.
Originally made to celebrate their 100th anniversary, this ink comes in a vintage-style bottle with a narrow neck with a marble stopper, to create a well at the top to aid in filling pens.
The Denneweg in The Hague is an old street in the center of the capital city. There are several buildings from the 18th century. (Source: Wikipedia) Ackerman