Korva is a scroll of the internet’s best ideas.
A squeezed rubber bag fills pens
Before the sac
Before this, writers dipped a pen into an inkwell, wrote, and dipped again. Dipping works because surface tension makes the ink cling to the pen. The line started out splashy and got more scratchy and scratchy until it faded away and it was time to dip again.
How the bag fills
The Waterman's chamber is a little rubber bag that can be compressed. Flick the lever on the side up and you compress the bag inside. Dunk the pen into a pot of ink and open the bag back up, and the vacuum floods ink in. That was a big innovation in how to fill pens.
Other fillers
Parker's Duofold works on the same idea with a button, and Pelikan patented a way to fill a chamber in the 1920s by unscrewing and screwing, which creates a little vacuum. Each one physically makes a space larger and smaller to back-fill it with ink. The weakness is that the rubber inside can perish.
How does releasing the bag draw ink in?
Squeezing the sac pushes air out through the nib. When the sac is released, its rubber springs back toward its original shape, which leaves lower pressure inside the pen than outside. The atmosphere, at about 101 kilopascals at sea level, then pushes ink from the pot into the empty space.
Why does old rubber perish?
Natural rubber is made of long, flexible polymer chains. Oxygen, ozone, light, and heat slowly break those chains and add cross-links, which turns the rubber hard, brittle, and cracked. Ink can attack it over the decades too. Many modern replacement sacs are made of silicone, which resists that kind of breakdown.
What replaced rubber sacs in pens?
Piston fillers use a threaded plunger that works like a small syringe, moving air and ink in and out of the chamber. Cartridges arrived widely in the 1950s, letting writers swap in a sealed ink supply without touching a bottle. Many pens today take either a cartridge or a converter that works like a piston.
More from The Rest Is Science
