In Part 1 of The Ink Story I was talking about how Ink occurred. During centuries there were many iterations about How to use Ink in the best way possible. So in this 2nd Part I will talk about pens.
The 19th century saw a big surge in fountain pen patents. But while they all had free-flowing ink, so that the ink didn’t all rush out at once, making an enormous blob on the page. They couldn’t just make the opening to the reservoir of ink very small: a tiny hole blocked the ink from coming out at all, and with a medium-sized hole it glugged its way sporadically on to the page. The reason for this behavior, which fountain pen inventors were slowly beginning to understand was the influence of air and the formation of vaccums inside the ink reservoirs.
When you try to pour liquid out of a container, you have to replace it with something, otherwise a vacuum will form inside the vessel, preventing any more liquid from flowing out. You’ll notice this if you try to drink from a bottle while covering the whole aperture with your mouth; the liquid comes out in glugs as the air fights to get in to replace the liquid you’re drinking. Each glug corresponds to air forcing its way into the bottle and, as it does so, it keeps the liquid from coming out. They take it in turns – liquid out, air in, liquid out, air in, glug, glug, glug. If you leave the mouth of a bottle partially open as you drink, then you’ll be able to drink continuously, without any glugs, because the air can flow in more smoothly. That’s why it’s easier to drink from wide-mouthed vessels, like cups and glasses.
But early fountain pens didn’t have any mechanism for getting air into the reservoir of ink, so it was hard to get a consistent flow of ink on to the page. Putting a hole in the top of the reservoir seems like the obvious solution, but if you turn the pen upside down, it will leak everywhere. The problem left everyone pretty flummoxed, until 1884, when an American inventor named Lewis Waterman perfected the design for a metal nib that allowed ink to flow down a groove by a combination of gravity and capillary action, while incoming air passed through in the opposite direction towards the reservoir.
His design brought in a golden era of fountain pens, the mobile phone of their age, transforming the way people communicated, and making pens a highly coveted possession. Having a fountain pen signified you were important – you were someone who needed to be able to write anywhere, anyplace, anytime. Just like the early mobile phones, or the first laptops, or any number of gadgets that have come since: it was cool.
But inevitable, there was another problem. Gall inks are often highly acidic, so they corroded the new metal pen nibs. They also often contained small particulate matter, which was visible in the ink when you wrote on the page, or clogged up the nib so the ink couldn’t come out. People would shake their pens in rage, trying to dislodge whatever unseen obstacles were mucking up their writing, but in the process, would lob ink across cafés or on to the clothes of unsuspecting passers-by. The fountain pen may have been perfected – the ink was not. It was time to replace gall ink.
But that was a complex problem. The particular chemistry of an ink and its ability to flow within the pen but not corrode it, its reaction with the paper, its ability to create a permanent mark but also dry quickly all had to be considered at once – to use engineering jargon, it’s a multiple optimization problem. Ultimately there were many solutions, and each pen manufacturer incorporated a different one into their design, which is why, if you buy a fountain pen, the manufacturer will insist you use their specially formulated inks.
The Parker Pen company, for instance, developed Quick Ink in 1928 to combat the problem of blotting. They combined synthetic dyes with alcohol to create an ink that flowed well in the pen, but then dried very quickly when it came into contact with paper. Ultimately it also chemically attacked some of the plastics they’d started using to make pens, like celluloid. It also wasn’t water-resistant, so if the paper got wet, the ink would start flowing again, often separating out the individual dyes used to make up the ink – black ink would separate into yellow and blue, for instance – ultimately making the writing unintelligible. But despite all the problems, most pen manufactures were convinced that fountain pens were the future, and that optimizing the ink was the answer to a reliable portable writing instrument. But the Hungarian inventor László Bíró had a completely different idea.
He turned the optimization problem on its head. Before becoming an inventor, he’d worked as a journalist, and had noticed that the inks used by newspaper printers were excellent – they were extremely fast-drying and rarely smudged or formed blots. But they were too viscous for a fountain pen; they wouldn’t flow, and gummed up the pen. So he figured – instead of changing the ink why not redesign the pen?
László Bíró’s newspaper articles were printed on a press made from a set of rolls that press ink on to a continuous sheet of paper. In order to have the millions of newspapers needed to meet the demand across the country ready for overnight delivery, they had to be printed very quickly. The pages went through the press at a rate of thousands per hour, so it was imperative that the inks dry immediately, otherwise they would smudge as the pages were assembled into a newspaper. To meet that need, the printing ink that László admired so much was invented. As László considered how to make a better pen, he thought about ways of re-creating the printing process on this much smaller scale. He’d need some sort of roller that could continuously ink the pen tip; eventually, he hit upon the idea of using a tiny ball. But how to get the ink on to the back so it could then be used to roll the ink on to the page?
He’d assumed that the printer inks would be too thick for gravity to pull the down from the pen’s reservoir on to the ball. But a strange piece of physics came to his rescue – non-Newtonian flow. There’s a relationship between the speed of a liquid’s flow and the sheer force that’s exerted on it – what we call viscosity.
So thick liquids like honey have a high viscosity, and flow slowly, while runny liquids like water have a low viscosity, and flow quickly under the same force. For most liquids, if you increase the force you’re applying to them, the viscosity will remain the same. This is called Newtonian flow.
But some liquids are strange; they don’t play by the rules of Newtonian flow. For example, if you mix cornflour with a bit of cold water, it forms a liquid that’s runny when you stir it gently, but if you try to stir it quickly, the liquid becomes very viscous, to the point that it behaves like a solid. You can punch its surface, and it won’t splash at all, but rather resist your fist as a solid does. This is what we call non-Newtonian behavior – the liquid doesn’t have one viscosity that determines its flow.
That cornflour liquid is sometimes referred to as oobleck (the name having come from a Dr. Seuss book called Bartholomew and the Oobleck). Oobleck’s non-Newtonian behavior is entirely due to its internal structure. On a microscopic level, the oobleck is full of tiny starch particles, where the cornflour is suspended very densely in water. At low speeds, the starch particles have enough time to find routes to flow around each other – a bit like passengers leaving a packed train. This is when they flow normally. But when put under pressure to flow quickly, as they are when you’re trying to stir the oobleck quickly or punching its surface, the starch particles don’t have enough time to move around each other and so they’re stopped in place. And just as passengers at the back of a train cannot move if those at the front are stationary, so too does the thwarting of a few starch particles hold up the rest which is why the whole liquid locks up, becoming more and more viscous.
Oobleck is not the only non-Newtonian liquid. If you’re ever painted a wall with emulsion paint, you might have noticed that the paint is extremely thick when it’s in the pot, almost like a jelly. But if you follow the instructions on the side of the tin and thoroughly mix the plant, you’ll find that as you stir, the paint becomes fluid, and then turns back to jelly as soon as you stop. This is also non-Newtonian behavior, but here the liquid is becoming runnier as a result of the force exerted on it, rather than more viscous. Again the reason originates from the inner structure of the liquid. Emulsion paint is just water with lots of tiny droplets of oil held in suspension inside it. When the tiny droplets of oil are allowed to settle, they’re attracted to one other and form tiny bonds, trapping the water between them to form a weak structure – a jelly. When you stir the paint, the molecular bonds holding the tiny droplets of oil to each other are broken, releasing the water and allowing the paint to flow. The same thing happens when you put the paint under stress by spreading it on to a wall with a paint brush. But once the paint is on the wall, and it’s no longer under stress, the bonds between the droplets of oil re-form and the paint becomes viscous again, creating a thick coat that doesn’t drip. That’s the theory anyway; obviously it all comes down to how well the chemists who formulate the paint can control the bonds between the droplets of oil, their size and number. It takes a lot of work to get the balance just right, which is why it’s worth the premium you pay to get a good tin of paint.
Even if you are not a painter and decorator you will have come across non-Newtonian liquids in the kitchen; Like emulsion paint, tomato ketchup thins when it’s under stress. It won’t budge until you hit the bottle, putting the ketchup under enough shear pressure for it suddenly to thin and shoot out of the bottle. That’s why it’s so hard to control the rate at which ketchup comes out of the bottle – if the force isn’t high enough, it flows extremely slowly, but once you give it a big whack, the viscosity suddenly drops and it splats all over your plate.
One of the most dangerous kinds of non-Newtonian behavior occurs when you mix together sand and water, creating a substance that’s often called Quicksand.
Quicksand has semi-solid properties until put under pressure and then it thins out, turning it into a fluid liquid – so-called liquefaction. That’s why when you step into quicksand, the more you struggle and wriggle to get out, the more liquid thins and the further you sink. But no matter what you see in the movies, most likely you won’t die by sinking into quicksand; because it’s a liquid with a higher density than your body, once you’re submerged to your waist, you’ll float back up. Still, getting out is very hard, since if you don’t move, the liquid thickens and solidifies around you, and if you do stuggle, it thins, making it hard to get a solid foothold. In other words, you’re stuck until you’re rescued – and that’s when it gets deadly.
But more dangerous than quicksand is the liquefaction that occurs during earthquakes. Here, in another deadly example of non-Newtonian flow, the stress from the earthquake’s vibrations liquefies the soil, usually causing massive damage. Just look at the 2011 earthquake in New Zealand: it struck the city of Christchurch, causing significant liquefaction that destroyed buildings and spewed thousands of tonnes of sand and silt on to the city.
As it turned out, non-Newtonian thinning was exactly the property that László Bíró needed to make the thick newspaper inks work in a fountain pen. He hypothesized that it would allow the ink to flow easily while you were writing but then, once the ink was on the page, it would become thick and viscous again and dry into a solid so rapidly that is wouldn’t smudge. László started trying to make the perfect pen with his brother, who was a chemist; after many struggles, including having to emigrate to Argentina at the outbreak of the Second World War, they finally had something that worked. Their pens have a reservoir of ink that feeds a tiny, rotating ball; when you write with the pen, the ball goes round, putting the ink under enough pressure to change its viscosity, so it comes flowing out on to the ball. At that point, the ink goes back to being sticky and gooey, until it hits the paper and flows out again. When you lift the pen, relieving the ink of its stress, it becomes thick again, and the solvents in the ink, which are being exposed to air for the first time, quickly evaporate, leaving the ink’s dyes on the paper and creating a permanent mark.
Genius! As you might expect, over the years, the ingredients for such a high-performing ink have become trade secrets, but if you want to get a sense of just how good they are, write with a ballpoint pen on a piece of paper and then try to smudge it with your finger. It’s really hard. But that’s not the only advantage that the non-Newtonian ink in biro pens has over the more fluid inks in fountain pens. Because it doesn’t flow under capillary action, the ink doesn’t bleed as it seeps into the paper as it does with other pens. It’s been chemically formulated to have a low surface tension when it comes into contact with cellulose fibers, as well as with the ceramic powders and plasticizers that are added to the top surface of paper to make it glossy (the so-called sizing). Fountain pen inks and other fluid inks have a high surface tension with sizing, so the ink sits on top of them, and breaks up into small droplets.
If you’re ever tried to make notes on the front of a glossy magazine with a fountain pen or tried to sign the back of a credit card with one, you’ll have notice this – the ink doesn’t stay. But ink from ballpoint pens seems to dry anywhere and stay exactly where you put it – even if you write upside down – because it’s not flowing thanks to the force of gravity, but instead being rolled on to the page. If you try to write upside down, you’ll discover still another advantage of the ballpoint pen. Just like the fountain pen, it won’t work if a vacuum forms in the reservoir of ink. But it has a simple way of preventing that – the top of the reservoir is open to the air, and the ink is quite viscous and won’t flow without experiencing a lot of stress, so it doesn’t fall out. Neat, eh?
All that means is that, happily for the forgetful among us, you can leave a ballpoint pen at the bottom of your bag for months on end and it won’t leak and cover your stuff with ink. Even if you forget to put the top back on and the biro’s left sitting unprotected in your pocket, the ink won’t come out. So good is this concept, and so reliable is the ballpoint pen at writing even when the top has been off for months, that early manufacturers realized they didn’t really need to put a top on the pens at all. Why not just retract the reservoir and ball back into the main body of the pen when you’re not using it?
That’s easy enough to do, and so the retractable ballpoint pen was born. Click it, and you can write; click again, and the ballpoint is retracted. Oh, how the Caliph of the Maghreb would have rejoiced at the sheer non-messiness and the audible delight of the retractable ballpoint pen! (as I mentioned his cause in Part 1 of the Ink Story).
The Bíró brothers produced the 1st commercial ballpoint pen after they’d emigrated to Argentina. They sold tons of them, to any number of clients, including the Royal Air Force, to be used by their navigators, replacing the fountain pens they had been using, which always leaked at high altitude. According to the biggest manufacturer of ballpoint pens on the market today, the French company BiC, more than 100 billion pens have been made since they were 1st invented. László Bíró died in 1985, but his legacy lives on. In Argentina they celebrate Inventors’ Day every year on the anniversary of his birthday, 29 September, and to this day in Europe we call ballpoint pens the biro.
Of course, despite its success many people hate biros. They decry the invention of the biro, saying it defiled the art of handwriting. It’s true that the price for creating a portable anti-smudge, anti-leaking, long-lasting, inexpensive, socially inclusive pen has been that the thickness of the line created is invariant. Line thinness is determined by the size of the ball bearing at the tip, and because a ballpoint’s ink doesn’t flow once it’s deposited on paper, the thickness of its line won’t change by slowing down or speeding up your writing as it would with the fountain pen, or other pens using Newtonian ink. Writing from ballpoint pens is more utilitarian, less expressive of an individual’s writing style. But personally I think it ranks up there with the bicycle for its impact on society. It’s a piece of liquid engineering that’s solved an age-old problem, has produced something utterly reliable, and is available at a price that is so affordable, most people regard, ballpoint pens as communal property.
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