The phrase “safety” means the pen has the ability to fit the nib of the pen securely in an airtight manner, ensuring safety with respect to ink leakage. Something taken for granted with contemporary pens but a major issue back in the day.
The cap is an essential, integral part of any fountain pen. Its function is to protect the nib and feed from damage and provide a simple and effective means for confining the ink which may collect around the pen at the base of the section. Thus preventing the ink from staining everything the nib touches. Not all caps include the additional component, an inner cap.
The cap, therefore, comprises the cylindrical cover which fits over the barrel and nib and an inner cap that encloses the nib and forms an hermetical seal with the leading edge of the section. The inner cap is also credited with slowing down ink evaporation thus improving the pen’s readiness to write.
In 1908, Waterman began marketing a safety pen for pens without retractable nibs. The pen included a revolutionary screw-on cap with an inner cap that sealed the nib by bearing against the leading edge of the section. Effectively preventing leakage, such pens were marketed as “safety pens.” Parker followed soon after with the Jack-Knife Safety and Mabie Todd with the Swan Safety Screw-Cap.
Safety Pens are equipped with a safety filling system in which the nib is retracted or extended with the rotation of a knob attached to an endless screw. But, not all safety pens include an endless screw mechanism.
Moore marketed a safety pen known as the Non-Leakable Filler, by which a longitudinal slide controls the movement of the nib. This movement of the nib and feed is achieved through the use of a sleeve on the aft end of the pen which slides back and forth on a shaft similar to the endless screw mechanism. In both designs, once the nib is in the retracted position, the pen can be inked or safely sealed.
Fun Fact: Moore was so confident in their non-leak filler, they shipped pens from the factory already filled with ink.
The safety filling system is an evolution of the eyedropper filler system. It simplifies the filling operations, eliminating the need to remove the section and nib unit and avoiding ink leakage as a result of differences in pressure and temperature. The opening left by the vacated nib unit provides the opportunity to ink the pen using an eyedropper. This also means there is less volume within the barrel available for the ink, as the inside of the barrel is also occupied by the mechanism and the nib unit.
Once the nib has returned to the inside of the barrel, the pen is hermetically sealed using a flat-bottomed cap equipped with a suitable gasket to prevent leakage. In fact, there is no possibility that the ink, due to pressure imbalances, and deposit in the cap, since pressure imbalances are immediately eliminated when the cap is loosened and the seal broken. The hermetical seal also reduces to near zero the possibility of ink evaporation.
The charm of the safety filling system lies in the mechanical complexity, which illustrates the pinnacle of the technology at that time. Whereas the mechanical simplicity of the non-leakable system makes it more robust and easy to manufacture. All that was required was good precision to machining tolerances and quality gaskets.
Origins of the safety filler are found in the United States during the last decade of 1800 and mass-marketed by Waterman. The design enjoyed greater success in Europe, where at the beginning of the last century practically all producers (particularly the German ones, including Kaweco), made use of this system. The non-leakable system was also used by Montblanc in their first Rouge et Noir models, most likely brought to Germany by Arthur Eberstein, founder of Montblanc who had previously worked for the Moore.