Mokumegane Kyuseido Kosumi FS
The Kyuseido Kosumi FS is the second fountain pen model from Kyuseido. “Kosumi” is the name of a move from the ancient game of Go, played as an extension of a previous move. The Kyuseido Kosumi FS features a 9 faceted cap design, introducing brutalist design to the elegant round barrel.
Mokumegane is an artisanal Japanese metalworking technique taking several different metals and forging them into a single piece of material. The word Mokumegane (木目金) translates to “Woodgrain/Woodeye” (Mokume - 木目) “Metal” (Gane - 金) and is characterized by its distinct woodgrain pattern formed by the layering of different metals. Traditionally, Mokumegane has been used in ceremonial objects such as sword hilts, vases, and even early types of portable writing instruments called Yatate. Today, Mokumegane is most often used in jewelry, especially wedding bands, in Japan. It is particularly favoured for the unique patina that it can take as each metal will patina at a different rate and into a different color and look.
Our Mokumegane pens use brass, copper, and cupronickel to give a unique woodgrain pattern, and are finished with a machine brushed texture. This material is not something that can simply be melted into a workable piece of metal. Instead, a difficult and arduous solid state diffusion bonding is used to laminate the various different metals together under heat and pressure. Each metal has a different hardness and will wear and patina differently to each other, which will create a unique tactile material through time.
As this is an artisan material, no two pens are identical and will have their own unique expressions and imperfections but all of these pens will evolve with the user to become pieces of art in their own right.
The Mokumegane is also available in the Kyuseido Kakari FS model.
ABOUT THE PUMP PISTON FILLING SYSTEM
The filling system that we deploy in the Kyuseido Kosumi FS is called the Pump Piston Filler. The idea is simple, you hook the piston rod onto the piston unit and unscrew it from it’s locked position. Once unlocked, you simply push the piston forward towards the nib section, submerge the nib into ink, and pull upwards to create a vacuum that draws ink into the pen barrel. The result is a full fill in a single stroke. To clean the pen, perform the same action as you would when you fill the pen, but instead of submerging the nib into ink, pump the piston with water and the pen will be clean in several quick pumps. While we don’t recommend it and it will void the warranty, it is also possible to remove the nib section to fully access the pen barrel to thoroughly clean a staining ink or pigmented/shimmer inks if needed.
Each Kyuseido Kosumi FS is fitted with a 14k gold nib and an ebonite feed, both designed for Kyuseido. The iridium tipping is premium and hard AM tipping that is formulated to last a lifetime. The Kyuseido Kosumi FS can be ordered with many nib customizations ground by our expert nib technicians at Kyuseido.
The filling system is inspired by Patent US610818 filed by George H. Means in 1898. The patent details a filler very similar to our design, but instead advocates for a threaded piston plunger. While Means never managed to bring the product to market as far as we are aware, at least two other companies have realised Means’s design of a threaded piston plunger and made them available to the market. The challenge of Means’s design was that it would almost be impossible to unthread the piston plunger from the rod without the piston plunger spinning in place. The two companies that have taken Means’s design and improved upon it both rely on a locking mechanism that affixes the piston plunger onto the end of the pen near the piston knob.
The Pump Piston Filler, however, takes Means’s idea for a threaded piston plunger and turns it on it’s head. While the Pump Piston Filler does also have a locking mechanism to affix the piston plunger onto the pen barrel, it does not rely on the locking mechanism to dislodge the rod from the piston plunger unit. Instead, the rod has spokes that engage with a J hook, which allows for free and easy disengagement of the rod. This means that the piston plunger unit can be disengaged at any point of filling, which yields two functional applications. The first is that users can fill the pen with however much or little ink they would like without creating a large air bubble in the barrel. This prevents unwanted burping of the pen, which is caused when excess air in the barrel pushes ink out of the pen due to changes in air pressure. The second is that based on where the piston plunger unit is disengaged, users can freely change the center of balance of the pen, which will give users a more comfortable writing experience based on their own preferences. Kyuseido’s Pump Piston Filler is the first in the world to reimagine Means’s original patent in such a way, resulting in a design that is actually much closer to the original drawings detailed in Patent US610818. We brought modern materials and design together with the heritage idea created by Means and creating a simple yet effective complication that elevates the fountain pen experience.TECHNICAL SPECS
Capped Weight: 72.3g
Uncapped Weight: 40.8g
Ink Capacity: 3.5ml ~ 4.2ml
Section Diameter: 10.6mm ~ 11.9mm
Pen Barrel Diameter: 12.6mm ~ 14mm
