Indelible

I’ve previously read about the wonders of the ballpoint pen and its significant improvement over its predecessors. Yet I found myself entranced re-reading the history of inks and writing in Mark Miodownik’s Liquid Rules. There were many nuggets I had forgotten and others that were new to me. Along with the chapter on glue, it made me ponder the wonder of sticky molecules – fluid one moment, solid and stuck a moment later!

 

Let’s begin with ink. The trick: you need it to flow on to paper, then you need it to stick. Timing is everything if you don’t want to end up with ugly smudges! I learned that reed pens were used by the Egyptians circa 3000 BCE. The ink was made “by combining soot from oil lamps with the gum from the acacia tree, which acted as a binder.” The hydrophobicity of carbon meant you could mix it with water to get a flowing black ink. It was called gum arabic, and can be found in art shops today. Problem #1: carbon ink doesn’t dry fast and can smudge. Problem #2: once dry, it doesn’t bind strongly to the surface, so you can scratch it off – but perhaps that’s a feature rather than a bug.

 

The next revolution was gall ink. (A gall is an oak apple.) Used in biblical times up to last century, it’s a clever bit of chemistry. Miodownik writes: “You make gall ink by putting an iron nail in a bottle with some vinegar; the vinegar corrodes the iron and leaves behind a red-brown solution, full of charged iron atoms… It reacts with the tannic acid from the galls and produces a substance called iron tannate, which is highly water-soluble and very fluid. When iron tannate comes in contact with paper fibers, it flows, through capillary action, into all the small crevices in the paper, distributing itself evenly. And as the water evaporates, the tannates are deposited inside the paper, leaving a lasting blue-black mark.” It's permanent ink. It’s also why substances with high tannin content, “red wine and tea can leave such bad stains on your clothes and teeth.” We also have historical documents of people complaining (by writing with that same ink!) how the ink got all over the place and was hard to wash off. We need a better delivery device.

 

The fountain pen was invented as early as the tenth century with many updates over subsequent centuries. You now didn’t need to carry an ink bottle with you with the ink self-enclosed in the pen. But there were problems: “controlling the flow so that the ink didn’t all rush out at once [made] an enormous blob.” It took a while for inventors to figure out that the problem was the seemingly random formation of air (vacuum) pockets. Miodownik illustrates this by describing the glugging that ensues: “Each glug corresponds to air forcing its way in… and as it does so, it keeps the liquid from coming out. Take it in turns – liquid out, air in, liquid out, air in, glug, glug, glug.”

 

A simple solution might be to put a hole at the other end, but then if you turn the pen upside down the ink leaks. Eventually a clever design by Lewis Waterman in 1884 utilized “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”. The problem: the acidic gall inks eventually corroded the metal nibs. Miodownik writes: “People would shake their pens in rage, trying to dislodge whatever unseen obstacles were mucking up their writing, but in the process, they would lob ink… onto the clothes of unsuspecting passers-by.” Having been ‘forced’ to learn how to write with a fountain pen in grade school (why, oh why?), I can relate. I’m glad when my school gave up on it after a year and we went back to ballpoint pens.

 

So back to inks. Quink was developed by the Parker Pen company. It was a “blend of synthetic dyes with alcohol… flowed well in the pen… dried very quickly when it came into contact with paper.” But there were problems. The solution of Laszlo Biro was to redesign the pen. From his knowledge of how the newspaper printing press worked, he eventually hit on using a tiny ball as a roller to deliver ink to paper. And this works beautifully because of non-Newtonian flow. Miodownik goes into detail explaining the relationship between viscosity and flow of liquids. Some liquids behave strangely: “if you mix cornmeal 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.” Emulsion paint is another non-Newtonian liquid: thick in the can, fluid when stirred, but then thickens again quickly and doesn’t drip! Quicksand is also a non-Newtonian fluid: If you’re in it, it flows under pressure when you move, then reverts to semi-solid when you don’t. So you get stuck!

 

Ballpoint pens are a beauty, thanks to these non-Newtonian liquids. They don’t smudge easily and “the ink doesn’t bleed as it seeps into the paper… 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…” You can even write upside-down against the force of gravity. You don’t even need a cap for the pen. All this and more can be found in chapter ten of Liquid Rules, aptly titled “Indelible”. I expect to refer back to it again in the future!