The TWSBI Diamond 580 IRIS is a fountain pen with a piston-filling system made of transparent polycarbonate, now with an iridescent finish, resulting in rainbow-coloured details. The cap is smooth while the barrel is faceted and has a diamond pattern (hence the Diamond in the name), and the clear barrel shows the piston mechanism and the ink level.

The TWSBI Diamond 580 is a high-quality writing instrument that features a piston-filling system, allowing for easy use with bottled ink. By simply dipping the nib into the ink and turning the piston knob, ink is directly drawn into the body, providing a generous ink capacity and an enjoyable refilling experience. TWSBI, which stands for ‘San Wen Tong (Hall of Three Cultures) reversed, is a brand created by Ta Shin Precision, a company with over 40 years of manufacturing experience and a history of producing high-end pens for other brands.

The pen is available in several nib sizes, it can be entirely disassembled for cleaning and servicing. The Diamond 580 features metal accents on the cap, grip section, and around the piston knob. The steel nib is smooth and quite wet and matches these accents well. Additionally, the Diamond 580 fountain pen can be attached directly to the TWSBI Diamond 50 ink bottle for easy refilling.