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(This page revised March 16, 2016)
For the first few decades after the invention of the fountain pen, pens were made of hard rubber and had caps that slipped on to cover the nib area. Hard rubber slip caps are not particularly reliable; they can slip off as easily as they slip on. If a cap slips off in the user’s pocket, the pen can dye a significant portion of the user’s clothing before the loose cap is discovered. The solution to this problem, first developed in the 1890s, was to create a pen whose cap screwed on instead of slipping on. A pen with a cap that can be screwed tightly enough on that friction keeps it from coming off is “safe” from leakage. Before the word “leakproof” came into use in the 1920s, the term “non-leakable” was used to describe pens of this type. Because a pen that does not leak can be carried safely, non-leakable pens quickly became known as “safety” pens.
The illustrations in this article depict pens with their proportions altered for illustrative purposes.
Possibly because caps had vent holes to prevent them from sucking ink out of the pen when removed, it does not seem to have occurred to the inventors of the early safety pens that they could simply thread the pen’s barrel where it joins the section and thread the cap at the corresponding location, adding a positive stop in the form of an inner cap that mated against the end of the section to prevent leaks This would have entailed another minor change, moving the vent holes (also called breather holes) down so that they were below that stop. This design did begin appearing around 1905-1910 (U.S. Patent No 764,227 by August Eberstein, issued in 1904), and it evolved into the screw cap that we know today. Shown here is a cross-section of a pen similar to a 1921 Parker Duofold, illustrating this type of cap:
The end of the section is flattened to form a table against which the end of the inner cap butts firmly enough to make an ink-tight seal. The inner cap, screwed tightly together with the main cap and clamping the clip between them, comes to a stop and seals against this table, and the pen is proof against leakage from the cap. The vent holes are in the unsealed area, so that air can be pulled in as the pen is uncapped, preventing the cap from sucking ink out of the pen as it is removed. The threaded area inside the cap, into which the barrel screws, extends farther up inside the cap than necessary to work around any problem of manufacturing tolerances that would stop the barrel from screwing in far enough to seal the inner cap against the section table. In the case of a button-filling pen like the one shown, the blind cap screws tightly against the back end of the barrel to prevent a leak there should the sac fail.
For arbitrary reasons, modern collectors restrict the term “safety” to pens with retractable nibs. The remainder of this article describes the two schemes that were devised in the late 19th century and used for several decades thereafter.
Morris W. Moore’s Non-Leakable Safety Pen (U.S. Patents Nos 567,151 and 567,152, issued in 1896) was the second of the classic safety pen designs, but its simplicity dictates that it be discussed before its more complicated predecessor.
Moore’s pen, like the “regular” pens of its time, fills with an eyedropper. Instead of screwing the pen apart to fill it as with an ordinary eyedropper filler, you simply put the ink in through the opening the nib leaves when retracted. Below is a schematic drawing of Moore’s pen, with the operating parts colored for easy identification. The nib is mounted on a slender shaft (gray) that is also the feed. This shaft, called the nib carrier, runs the length of the pen’s barrel and out through an opening that is lined with cork (pink) to produce an ink-tight seal. At the end of the nib carrier is a knob (red); to retract the nib, you pull the knob. To provide a better finger grip and also to protect the nib carrier, Moore attached a sleeve (green) to the end knob, calling it a slide; the slide rides along the outside of the barrel.
The retractable nib permits an ink-tight seal of the reservoir. When the nib is retracted, the end of the barrel forms a conical opening that is plugged tightly by a short cylindrical projection on the inside of the cap (orange), creating a seal that does not permit ink to escape to the outside.
Thus, as long as the cap remains secure, there is no risk of leakage with the pen in any attitude. The American Fountain Pen Company, maker of Moore’s pen and renamed in 1917 to become the Moore Pen Company, was not slow to point out this advantage in its advertising:
“Every person that has carried a Fountain pen realizes the necessity of carrying it in the pocket POINT UP, as directed, or their clothing will soon be badly soiled with ink; also their hands when using it. NOT SO WITH THESE PENS. Being AIR and INK TIGHT, they can be carried in ANY POSITION IN ANY POCKET when filled with ink, and cannot leak…”
Other safety-pen manufacturers made the same point in different words.
The safety principle addresses leakage in the pocket, but how does Moore’s pen keep itself from leaking when the nib is extended? The exterior of the collar that secures the nib to the nib carrier is a very close fit in the open end of the barrel. When the nib is extended, the friction between these parts holds the nib in position, and whatever gap is left between them is small enough that capillary action and the partial vacuum inside the pen prevent the ink from leaking out.
In the drawings above, you will notice a long slender pin, the nib safety pin, inside the cap. This pin was not part of Moore’s original design; it was added by the engineers of the American Fountain Pen Company as they developed Moore’s concept into a workable product. As its name implies, it was a feature to protect the nib. If the user started to cap the pen without first retracting the nib, this pin would push against the end of the nib carrier and force the nib to retract. Because of its length, however, in shorter pen models the pin would also prevent the cap from seating fully on the knob at the back end of the nib carrier when the user posted it. As illustrated in this article, these shorter pens have a corresponding hole drilled into the end of the knob to provide the necessary clearance.
In Moore’s pen, the nib is held in the extended position only by friction between the nib carrier and the barrel opening, with a slight assist from the packing that seals the back end of the barrel. This system works quite well, but a more positive design holds a certain attraction to those who might be unwilling to trust the simple Moore. “More positive” implies ”more complicated,” and Waterman’s Ideal Safety Pen is definitely more complicated.
The first truly “safe” pen to appear on the market, before Moore got there, was patented by Edward G. Peck and Frederick O’Meara in 1894 (U.S. Patent No 523,234) and improved the next year by Peck and Henry Horton, who set up a company to make pens to the design (U.S. Patent No 551,895). Francis C. Brown improved it further, and it reached what might be considered its apex in the implementation produced by L. E. Waterman from about 1907.
As described at the beginning of this article, simply relocating the vent holes did not occur to Peck, O’Meara, Horton, Brown, or the engineers at Waterman. Instead, the basis of all the variations on the original Peck/O’Meara design was a retracting nib, with a cap that sealed the opening left when the nib was retracted. Illustrated here is Waterman’s second implementation of this system, with the operating parts colored for easy identification.
Based on patents by Brown (U.S. Patent No 612,013, issued in 1898, and U.S. Patent No 949,752, issued in 1910), Waterman’s pen uses a long-pitch screw mechanism (a helical cam) within the barrel to extend the nib.
A hard rubber pin (yellow) secures the operating knob (green) to the internal shaft (blue), and a cork packing (pink) seals the shaft where it passes through the barrel cap (red). The barrel cap screws tightly against the barrel to provide a seal at that joint. (No sealant or adhesive of any kind is used.) Two grooves run lengthwise along the inside of the barrel (shown along the top and bottom in this drawing). A sliding nib carrier (gray) holds the nib and feed, and a crosswise pin (purple) through the back end of the carrier rides in two long helical slots in the tubular portion of the blue shaft. The pin extends far enough through the shaft to engage the grooves in the barrel. The knob is just the right diameter to wedge gently into the cap (orange) when the cap is posted (enabling use of the cap as a knob that is easier to grasp). Turning this unit forces the pin to slide along the barrel grooves, and this action extends or retracts the nib.
As with Moore’s pen, the retracted nib in Waterman’s version leaves a conical opening that is plugged tightly by a short cylindrical projection on the inside of the cap (orange), providing an ink-tight seal when the pen is capped.
Instead of relying on the fit between the nib carrier and the barrel opening as Moore’s pen does, Waterman’s pen has a tapered seat at the front of the barrel against which the nib carrier mates firmly to provide a positive seal against leakage when the pen is in use.
In its first implementation, Waterman had interchanged the locations of the straight and helical slots. With the helical slots on the barrel wall, the nib rotated with the knob as it was retracted or extended. This version was more costly to produce and more prone to jam when operated, and Waterman soon abandoned it, returning to the system described in the original Peck/O’Meara patent.
Moore’s pen went out of production in the mid-1920s. Waterman’s version lasted about a decade longer, and Waterman-style safeties have been made from time to time since then, even in the 21st century.
The information in this article is as accurate as possible, but you should not take it as absolutely authoritative or complete. If you have additions or corrections to this page, please consider sharing them with us to improve the accuracy of our information.