(Ron Gilmour is a fountain pen enthusiast, would-be calligrapher, and librarian. You can find him online at Twitter @gilmour70 and Instagram.)
In the introduction to this series, I mentioned that one of the drawbacks to the various sac-filling pens was ink capacity. Because you need room for the sac itself and whatever is compressing it, there's a limit to how much ink you can get into a sac-filling pen.
In the 1930s, Parker came up with an interesting solution. What if suction could be created in the entire pen barrel rather than just the sac? They replaced the sac with a flexible diaphragm at the rear of the pen. When the diaphragm was pushed inward by a plunger, air was forced out of the pen. When the diaphragm was released, ink was taken up. A breather tube was added to prevent ink taken up by one stroke of the plunger from being squeezed out by the next stroke. This innovative mechanism, eventually dubbed the "Vacumatic," allowed a far greater portion of the barrel to be filled with ink than any sac filler.
Another drawback of sac fillers was that it was impossible to see how much ink you had left. (Sheaffer tried to make lever-fill pens that would allow this, but were only moderately successful.) The smart people at Parker realized that once they had eliminated the sac, all they had to do was use some transparent material in the body and the ink level would be easily visible.
And that brings us to the pen's aesthetics. An innovative filling system and a visible ink supply were great, but the Vacumatic might not have been the success that it was if not for another factor: it was gorgeous. The alternation of solid and transparent bands of celluloid still turns heads today. (A friend refers to my silver Vac as "your Matrix pen.") The striking, arrow-shaped clip is a design element that Parker still uses on their pens today. The total package is an Art Deco masterpiece.