The Kaweco Royal Blue 50ml fountain pen ink refill provides a classic, brilliant, erasable blue color in a traditional glass bottle. With a 50ml capacity and a high-purity water-soluble formula, it ensures smooth ink flow through the nib without leaving deposits or stains. It allows for easy and economical long-term refilling of fountain pens with standard or mini converters. The royal blue shade is the international standard for school writing, university notes, and everyday correspondence on various paper qualities.