By TIJ Print Solutions
Every inkjet printer, from a desktop photo printer to a coder on a bottling line, depends on the same trick: getting a liquid off a nozzle and onto a surface without anything touching that surface.
That trick is far older than the computer. It started with transatlantic telegraph cables, ran through Victorian fluid physics and Swedish heart monitors, and passed through an Ohio courtroom that, in 1981, took the trouble to write much of it down. This is the prehistory of inkjet: the century of experiments before inkjet became an industry.
1867: Kelvin's ink that never touched
In the 1860s, the hardest problem in communications was the undersea telegraph cable. Signals that crossed the Atlantic arrived faint and smeared, too weak to drive the mechanical recorders used on land.
William Thomson, later Lord Kelvin, solved part of it in 1867 with the siphon recorder. A fine glass siphon drew ink from a reservoir and hung over a moving paper tape. The siphon was attached to a coil that swung with the incoming current. The clever part was how the ink reached the paper: Kelvin electrified the ink to a high voltage and grounded the paper, so electrostatic attraction pulled the ink across the gap. As one description puts it, "the siphon tube itself never touches the paper, only the ink."
The coil was so delicate that friction from a pen on paper would have distorted the signal. Removing contact was the whole point. The result was a wavy line, with the swings to either side marking Morse code's dots and dashes.
To be precise for the purists: this was not inkjet as we know it. Kelvin's recorder drew a continuous line, not drops. But it established two ideas that every later inkjet uses: put the ink on the surface without touching it, and use electric fields to control liquid.
1878: Rayleigh explains why a stream breaks into drops
If you've watched a thin stream of water from a faucet, you've seen it: smooth near the tap, then rippling, then breaking into beads. Joseph Plateau studied the effect experimentally. Lord Rayleigh worked out why in two papers, "On the Instability of Jets" (1878) and "On the Capillary Phenomena of Jets" (1879).
Surface tension wants a liquid to have as little surface area as possible. A long cylinder of liquid has more surface than a row of spheres holding the same volume, so any small ripple in the jet grows until the cylinder pinches off into drops. Rayleigh showed that the ripple that grows fastest has a wavelength about nine times the jet's radius, roughly four and a half jet diameters. Physicists now call this the Plateau–Rayleigh instability.
This is the physics underneath every continuous inkjet printer ever built. Left alone, a jet breaks up somewhat irregularly. Vibrate the nozzle at the right frequency and the breakup locks onto your signal: every drop the same size, the same distance apart, formed at the same point. By the 1890s, Charles Boys was doing it with a tuning fork, and seventy years later inkjet engineers built on his trick.
1948: a Swedish engineer's ink-jet heart monitor
The next step came out of medicine.
In 1948, Rune Elmqvist, an engineer at the Swedish medical-equipment company Elema-Schönander, developed a recorder for electrocardiograms that he called the Mingograf. His US patent, 2,566,443 (Swedish priority October 1948, granted September 1951), describes "a liquid jet recorder": a fine nozzle, mounted to swing with a galvanometer, spraying a thin jet of ink onto moving paper. Because the nozzle never touched the paper, there was no pen friction to blunt the fast details of a heartbeat trace. Siemens later sold the design as the Oscillomink.
Again, for precision: Elmqvist's jet drew a line by moving the nozzle. There was no charging and no deflection of individual drops. It is, though, an early commercial instrument that wrote with a jet of ink.
Elmqvist's next project is a better-known story. Ten years later, he built the first implantable cardiac pacemaker, implanted in a patient in Stockholm in October 1958.
The 1950s: charged drops, blue dye, and a teletype
By the 1950s, researchers were combining the pieces: drops, plus charge, plus deflection.
The court record of Mead Digital Systems v. A.B. Dick, which surveyed the prior art in detail, mentions a researcher named Magarvey who, in 1956, "deflected charged water droplets in a varying electrostatic field to separate some droplets from others which were intercepted." He added blue aniline dye to the water so the droplets would show up in photographs. As the court notes, he "did not disclose any printing or recording use for his device." He had essentially demonstrated the core of continuous inkjet without proposing a printing use.
Someone else did see the printing use. In the late 1950s, Charles R. Winston at Teletype Corporation built an ink jet printer that, according to the court, "sold commercially for several years as the Teletype Inktronic." His patent, US 3,060,429, was filed in 1958 and issued in 1962. It combined nearly the whole modern recipe: ink under slight pressure, uniform and highly charged droplets, paper moving across the path, some drops intercepted so they never reached the paper, and others steered by electrostatic deflection into position.
The appeals court later called Winston the first to build a commercially successful ink jet printer, and he did it before the patents most histories treat as the starting line.
1961–1965: Stanford and Lund
Two researchers then turned these experiments into the foundations of the industry.
At Stanford, Richard Sweet sketched a droplet-deflection apparatus in his lab notebook in July 1961 and got Army Signal Corps support for it through his group leader, R. C. Cumming. Sweet's key move, inspired by Boys' tuning-fork experiment, was to pair a vibrated nozzle with a charge on each drop set by the incoming signal. The vibrated nozzle locked the Rayleigh breakup to a fixed frequency, so every drop was identical and predictable, and could be charged and placed precisely. His patent, US 3,596,275 (filed 1964, granted 1971), became a foundational continuous inkjet patent. (The full story of Sweet, his patents, and how they split the industry in two is in another piece in this series, on Mead's DIJIT.)
In Sweden, at the Lund Institute of Technology, physicist Hellmuth Hertz, grandnephew of Heinrich Hertz, the physicist who proved radio waves exist, came at inkjet from medicine too. Hertz had produced the first echocardiographs with the physician Inge Edler, and needed better ways to record the signals. His patent with Sven-Inge Simonsson, US 3,416,153 (Swedish priority 1965, granted 1968), used an electric field to scatter charged drops away from the paper in a controlled way. Varying how many drops got through produced shades of gray, and the patent names color reproduction as a use.
Hertz's line went somewhere unexpected. His technology was licensed to Applicon, and in 1984 former Applicon staff founded Iris Graphics, whose Iris printers became famous in the art world for high-quality inkjet reproductions. Iris later passed through Scitex and Creo to Kodak, which put it in the same corporate family as the Dayton continuous inkjet business.
What the century added up to
By the mid-1960s, every element of continuous inkjet existed:
- Non-contact ink delivery (Kelvin, 1867)
- The physics of drop formation (Plateau; Rayleigh, 1878–79)
- A commercial jet-ink recorder (Elmqvist, 1948)
- Charged-drop separation (Magarvey, 1956)
- A commercial charged-drop printer (Winston's Inktronic, late 1950s)
- Controlled, synchronized drop formation with charge-and-deflect placement (Sweet, 1961–64)
- Grayscale by drop control, with color named as a use (Hertz, 1965)
What didn't exist yet was a business that could make it pay at scale. That came next: a duplicating company in Chicago, a paper company in Dayton, and a 1968 patent that split the field in two.
More inkjet history from TIJ Print Solutions: read the rest of the series →