(This page published May 1, 2019)
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In the imaginations of most people, heroes in the 1930s cowboy movie serials wore white hats (Hopalong Cassidy being possibly the sole exception), and villains wore black hats. The black/white dichotomy wasn’t really that clear cut, but that’s the convention that comes to mind, and it carried over to The Great Race, Blake Edwards’ 1965 homage to Laurel and Hardy in which the white-clad Great Leslie duked it out with black-clad Professor Fate in a round-the-world car race, and to TV cartoons, where Canadian Mountie Dudley Do-Right was perennially battling the mustache-twirling Snidely Whiplash to save Nell Fenwick. Following the convention a step further, into the world of fountain pen inks, we would find Parker “51” Ink wearing a two-colored hat.
What was the deal with “51” ink?
When it was introduced in 1941 together with the “51” pen, the ink was advertised as drying almost instantly, twice as fast as any ordinary ink — even Parker’s own quick-drying Quink. Given how the pace of life was speeding up through the 1930s, that was an obvious win: you didn’t have to wait even a few seconds while your ink dried, so there was no need to carry a blotter in your pocket or purse.
There were four colors of “51” ink:
The choice of colors, although ridiculously limited if judged by today’s standards, was also a win: not everyone likes blue or black.
Parker also emphasized that you were headed for disaster if you made the mistake of using “51” ink in any pen other than the “51”. Limiting the sale of your ink to only people who have bought one specific model of pen that you make seems like anything but a win, but that is what Parker considered necessary.
How did they do it? How did they make “51” ink dry so fast? It turns out, if you read between the lines, that they didn’t. It didn’t really dry any faster than an ordinary ink, at least not if drying means evaporation. What it did do, as they said right on the box, was to sink into the paper with incredible speed instead of sinking in slowly like ordinary inks, which relied primarily on the fluid remaining on the surface to evaporate. But how did it do that?
To understand how “51” ink worked, we need to understand a little about what an ink is. In most cases, a fountain pen ink is a solution. There are exceptions; but for the purposes of this discussion, we shall take it as read. In a simple solution, one component (water, for example) is a solvent. Another component (sugar, for example) is a solute, the stuff that dissolves in the solvent. When the solute dissolves, its physical structure breaks down to the molecular level, and its molecules mix on an equal footing with the molecules of the solvent. Water and sugar make sugar water, a liquid with no solid matter in it. Fountain pen ink is exactly like that, except that it contains more than one solute.
To ensure consistent behavior, ink makers start with distilled water. The principal non-water component in any ink is the colorant. In “51” ink, the colorant was an aniline dye that was quite happy to dissolve in water. I do not have a list of the dyes Parker used in red, green, and black “51” ink, but the blue dye was Direct Pure Blue 6X Extra Concentrated.
The other components in a basic ink are a wetting agent, or surfactant, and a biocide to kill mold. These two tasks were handled in “51” ink by a single solute, sodium hydroxide, NaOH, a strongly alkaline compound also known as lye or caustic soda. It is a near-perfect wetting agent; where water alone beads up on a gold nib, a dilute solution of sodium hydroxide will form a film over the nib’s entire surface. But that is not what you want in an ink. It flows like crazy, and that’s good, but it’s so wet that it also bleeds and feathers like crazy. And that’s bad.
Here is where “51” ink began to be radically different from ordinary inks. To counteract the extreme wetness of the sodium hydroxide, Parker added potassium amyl xanthate, CH3(CH2)4OCS2K, to tame the wild flow and the tendency to bleed, and ordinary corn starch to reduce feathering as much as possible. Amyl xanthate is soluble in water, but corn starch is not; it forms a colloid, slightly increasing the ink’s viscosity. To improve flow controllability, another colloidal material, a particular kind of clay called a bentonite was also included. (The specific bentonite chosen was Wilkinite.) The use of the two colloidal substances means that “51’ ink was not a pure solution; it contained solid matter.
The last piece of the puzzle concerned permanence. Aniline dyes fade over time, even when not exposed to light. (Fading is much more rapid when the writing is exposed to light.) In order to impart a more long-lasting quality to the ink, Parker added ammonium metavanadate, NH4VO3, a metallic salt that does not precipitate out of solution in an alkaline environment. As the dye faded away to invisibility, the ammonium metavanadate would gradually decompose, leaving a brown residue.
With all the components included, the next step was to determine how much of each to use, and that was merely a matter of experimentation. The following table lists the ingredients in blue Parker “51” ink together with their proportions in the mixture, as given in U.S. Patent No 1,932,248, issued to Carl S. Miner and Galen H. Saylor on October 24, 1933, and assigned to the Parker Pen Company.
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| Ingredient | Parts |
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| Direct pure blue 6X | 1.60 |
| Flake caustic soda | 1.30 |
| Ammonium metavanadate | 0.35 |
| Amyl xanthate | 0.02 |
| Corn starch | 0.05 |
| Wilkinite | 0.20 |
| Water | 100.00 |
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The proportions would be very similar, but not necessarily identical, for the other three ink colors. Differences would arise from the differences in behavior of the various dyes.
Why did Parker warn against using “51” ink in other pens? The principal reason was Parker’s own Vacumatic, whose body (including the barrel, which was the ink reservoir) was made of celluloid. “51” ink was alkaline, with a pH of about 11, roughly the same as that of chlorine bleach. In museum conservationists’ terms, the ink would cause irreversible damage to the molecular structure of the celluloid. In lay terms, the ink would dissolve the pen. Chlorine bleach will, too, if given enough time. (Consider this a warning not to clean your pens with chlorine bleach!)
It would be possible to use “51” ink in a sac-filling celluloid pen if you could be certain that the section and feed were hard rubber, not celluloid or a related plastic; but by the 1930s Parker was using plastic for sections and feeds, so even the sac-filling Parkette shown above would be destroyed by the ink. Likewise, Parker could not be certain about whether other manufacturers used plastic parts that would be exposed to the ink path — and there were many, including Eversharp, Sheaffer, and Waterman — so to protect itself from liability should other brands of pens be damaged, the company just said, “Do not use this ink in any pen except the Parker ‘51’.”
An important feature of the Parker “51” pen was its hooded nib. The shell (hood) was there to prevent evaporation. It was not superfast evaporation that was a concern, because that didn’t happen, but rather ordinary everyday evaporation such as any pen with an open nib would experience while it was being used. Evaporation of water from “51” ink would increase the concentration of the special ingredients, upsetting the chemical balance of the ink in ways that could alter its behavior. There is no way to prevent evaporation entirely, but the hooded nib, with a secondary supply of ink in the collector right behind the nib, minimized to the greatest extent possible the negative effects of what little evaporation could still occur.
With all the care Parker took, there was still a weak point. “51” ink tended to hasten the ossification of latex rubber. Parker advertised its Vacumatic (and the Vacumatic-filling “51”) as being sacless, but that was only about 95% true. The diaphragm, part of the filler pump, was made of latex rubber, and although it did not form the entire ink reservoir, it was exposed to ink. And it tended to ossify more rapidly under the chemical action of “51” ink than when used with other inks.
Parker recognized the diaphragm longevity problem, and in 1948, with the introduction of the Aero-Metric “51”, the company withdrew “51” ink, replacing it with a new ink called SuperChrome (U.S. Patent No 2,528,390, by Parker engineer Galen H. Saylor). The new ink came in a wider variety of brilliant colors produced by the use of copper-bearing dyes. Copper is an extremely active catalyzer of rubber, and SuperChrome ink also contained a chemical referred to as a copper inhibitor, whose purpose was to prevent (or at least severely retard) the action of the copper on rubber parts. Having solved that problem, however, SuperChrome ink, also alkaline like “51” ink, was eventually found to corrode the sterling silver breather tube in the Aero-Metric “51” (example shown below), and it was discontinued in 1956.
The ultimate answer to the question “Why not?” is that using inks known to cause problems, even if you have not personally experienced those problems, is asking for trouble. There are many excellent inks on the market that are known to be safe — why risk damaging or destroying an expensive pen? Many “51” owners figured that out, and since the pen has always worked perfectly well with other inks, they simply didn’t take any chances. They used known safe inks.
Parker’s engineers received a patent for the concept and formula for what would become “51” ink in 1933. The company then spent the next six years developing a pen that could safely use its revolutionary ink. Development of the pen was completed in 1939, the 51st year of the company’s existence, and that is why the ink and pen were named “51”. 
True for all but a very few fountain pen inks. Some inks , such as nanoparticle inks like Platinum Carbon Black, contain solid material that is produced as particles so fine that Brownian motion keeps them in suspension.
The word “merely” should not be interpreted to mean that the process was simple or quick. Changing the concentration of any one ingredient could have dramatic effects on the behavior of other components, resulting in the need for many tests over an extended period of time to determine exactly what would work as desired and what would not.
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.
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