Noodler's Polar Bulletproof, Eel Fountain Pen Ink - Black EEL INK  American-made eel inks contain added lubricants intended to keep piston-filled pens writing smoothly. With type of ink, the piston can maintain smooth sliding without becoming clogged. WATERPROOF - Bulletproof inks are resistant to water and tools of forgery such as bleach, alcohol, and UV light. These inks use cellulose-reactive dyes and work best on uncoated and cellulose-based papers. FOR FOUNTAIN PENS  This ink is suitable for fountain pens, calligraphy, and piston-filled pens. For pens with skip-prone nibs, a permanent regimen of Eel Black can make them write consistently. ARCHIVAL QUALITY  Long lasting, fade-proof, and true black. This ink is eternal meaning it is permanent, matte, lightfast and perfect for important documents. FREEZE RESISTANT - This ink is formulated to resist freezing at very low temperatures. This ink may form some harmless ice slush at very low temperatures, but it will not expand.