How Printer Ink Works

Think of the ink in your printer as a sort of bridge between your ideas in the digital world and their realization in hard copy.
Think of the ink in your printer as a sort of bridge between your ideas in the digital world and their realization in hard copy.
Image by HowStuffWorks/HP

You're up late at night working on that last-minute school paper. A wave of relief washes over you as you make the final edit and hit save. But when you go to print, you get a message informing you that your printer is out of black ink and it won't budge. At this point, it is either off to a copy shop with your document on a thumb drive or to a 24-hour big-box store that sells printer cartridges, you hope, for your model.

A printer is an extremely useful computer peripheral, but it's one that we sometimes love to hate. They produce frustrating incomprehensible errors, such as "PC Load Letter." Sometimes our computers have issues seeing them so that we can send them print jobs. And they periodically get paper jams. They're also notorious for running out of ink the moment you need it most (despite any early warning messages we might have brushed off).

The most common desktop printers are inkjet and laser printers. Inkjet printers use cartridges that are filled with liquid ink (usually), and laser printers use cartridges filled with powdered toner. How long these cartridges will last depends on myriad factors including the model of your printer, what cartridges you bought, how much you print, and how often you use or turn off your printer.

But printers also allow us to fill blank pages with text and images that weren't there before, and the technology behind the devices — and the ink they spew — is pretty impressive. They've come a long way in the past few decades.

Early Desktop Printers

Scottish mathematician and physicist William Thomson, Lord Kelvin, was working on the precursor to the inkjet printer in the 1860s.
Scottish mathematician and physicist William Thomson, Lord Kelvin, was working on the precursor to the inkjet printer in the 1860s.
© Universal History Archive/Getty Images

Although there were commercial and industrial printers for use with large, expensive computers for decades beforehand, the golden age of the printer really began when personal computers entered the market in the 1970s and 1980s. Computers were coming into the typical office and even the home, and other peripherals, including printers, were developed to use right alongside them.

Most of the early printers for personal computers were very noisy impact printers, including dot-matrix and daisy-wheel, both introduced in the early 1970s. The former type drove print head pins into an ink-infused ribbon to get ink onto the page, and the latter drove a wheel of pre-formed typewriterlike characters into the ribbon. But in the mid-1980s, consumer inkjet and laser printers were introduced nearly simultaneously, and they eventually took over a large percentage of the printer market.

Inkjet printers were under development in one form or another for almost a century before they actually came out. Around 1867, a patent was granted to William Thomson (aka Lord Kelvin) for a device that would have used electrostatic technology to print telegraph messages using ink droplets on a continuous roll of paper tape. Siemens released the first continuous inkjet printer in 1951 for use in medical records coding, and continuous inkjet printers are still used for commercial purposes.

Breakthroughs in drop-on-demand inkjet technology, however, made the devices viable for home and small office use. In the 1970s, companies were researching piezoelectric methods for accurately releasing ink onto paper in precise droplets, and Canon and Hewlett-Packard began independently working on methods to do the same using heat instead. The research also extended to development of inks that could withstand heat and light, would properly adhere to the paper and would dry quickly, among other traits.

Hewlett-Packard introduced the ThinkJet inkjet printer to the market in 1984, which used disposable cartridges full of ink, replacing their earlier serial dot-matrix printers. Canon released the BJ-80 inkjet printer (using what they called Bubble Jet technology) in 1985. Epson released the SQ-2000 printer (called IP-130K in Japan), which used piezoelectric rather than thermal technology, in 1984. They were all monochrome printers, which used a single shade of black ink.

Inkjet's cousin, the laser printer, had its roots in a copier machine technology called electrophotography, or xerography, which involved electrical charges, light and powdered toner (rather than liquid ink). The method was invented by Chester Carlson in 1938 and was first used in the Xerox 914 copier in 1959. The first laser printer was released by IBM in 1975 and worked with their mainframe computers. Hewlett-Packard released its LaserJet printer in 1984. Early laser printers had much better resolution than their inkjet counterparts and sold better.

Other types of printers were in the works around the same time as drop-on-demand inkjet printers and laser printers, and some came to fruition and are still in use for various purposes. Thermal transfer printers use heating pins to melt a solid waxlike ink housed on a ribbon or in sticks onto paper. Dye-sublimation printers transfer ink from a printed roll of film to another material by heating the ink so that it turns directly into a gas. And some other thermal printers burn dots onto special paper that changes color with the heat (requiring no ink at all). There are even still dot-matrix and daisy-wheel printers in use in some industries for things like check and invoice printing.

But inkjet printers caught up with and surpassed all other types, even laser printers, starting in the mid-1990s when color inkjet cartridges were added because of their lower cost, ever improving resolution and ability to print in vivid color.

About 90 percent of the inkjet printers sold globally in 2014 were still made by pioneers Canon, Epson and Hewlett-Packard. They aren't the only game in town, however, with Brother, Samsung and others producing them as well. Lexmark and Kodak both stopped selling printers in 2012 [source: Collinson].

Inkjet and Laser Printer Functionality

Multi-function devices like this one, which can print, fax and scan, are moving into the spaces once held by stand alone printers.
Multi-function devices like this one, which can print, fax and scan, are moving into the spaces once held by stand alone printers.
Image by HowStuffWorks/HP

The two printers that are most widely available and cost-effective for home and typical office use are inkjet and laser printers.

Inkjet printers spray liquid ink onto paper in tiny, precise drops. The ink is held in replaceable or refillable cartridges, most of which include a print head with an array consisting of hundreds or thousands of tiny nozzles through which the ink is sprayed, and which are arranged close together. Some printers have built-in printer heads that are separate from the color cartridges. The cartridges also include microchips and other tiny electronic components to control the ink spray and may include hydrophobic foam that holds the ink. These printers usually use either thermal technology (using tiny chambers of ink that heat up) or piezoelectric crystals (which vibrate or change shape when charged) to propel tiny ink droplets onto a page to create the printed text or images. A printer arm moves the cartridges across the page as the images are drawn. Software algorithms that interpret the computer image you are trying to print determine the color and position of the ink that makes it to the page.

The ink in a typical inkjet printer includes black plus three primary colors with which all the other printable colors are made through blending. These primary colors are cyan (blue), magenta (a reddish color) and yellow. Black ink is usually in its own cartridge. For some printers, the other colors are housed in a single cartridge, while for others, each color has its own separate cartridge.

Inkjet printers can print on a wide variety of media, including various weights of paper and specialized materials like iron-on transfers, cloth, canvas, transparencies, and CD or DVD labels. There are inkjet printers dedicated entirely to printing photographs on special photo paper, some of which have more than the three primary colors for more photorealistic color possibilities.

Laser printers use powdered toner made of tiny particles of colored plastic rather than liquid ink. Lasers project an image onto a rotating drum or belt coated in a photosensitive material, changing the charge in those areas. The toner is charged with static electricity of the opposite polarity, and when the drum is rolled through the toner, the toner is attracted to the image area created by the laser. The toner-covered drum is pressed onto a sheet of paper, which has a charge opposite to that of the toner applied to it so that the toner is then attracted to the paper. The paper is heated and pressed through rollers so that the toner melts and the image fuses to the paper. LED printers work similarly but use arrays of light-emitting diodes instead of moving lasers to project the image onto the drum. Most home-use laser printers are monochrome, but color laser printers exist, and they usually have a separate drum and cartridge for each color (black, cyan, magenta and yellow).

The various home and office printers also come with a variety of different functions. They handle various sizes and types of paper and other media. One that prints on wider paper, such as poster-sized, will be more expensive than the typical ones that mainly print on standard letter-size paper. Some also include duplexing (printing on both sides of the page). And many now have WiFi and cloud capabilities so you can send pages to the printer wirelessly. There are also a lot of multi-function devices on the market that act as printers, scanners, copiers and fax machines in one.

Inkjet and Laser Printer Quality Differences

The differences between the two make each better suited for different purposes. Laser printers are faster (printing more pages per minute), tend to produce higher quality results (with some exceptions) and are more well-suited for high-volume printing than inkjet printers. Laser printers also print much sharper lines and are therefore well-suited for text, logos and simple business graphics. The economical laser printers are mostly monochrome, however. Modern inkjet printers print both black and white and color these days, and they have an edge on laser printers for photo printing because they tend to blend colors better. There are, however, expensive commercial color laser printers that are good at printing photos.

Resolutions vary from printer to printer. They've improved greatly since those early 96-dots-per-inch (dpi) inkjets in the mid-80s. The first desktop inkjet printers only had 12 nozzles on the printhead, but new printers have hundreds, sometimes even thousands, all less than half the thickness of a human hair, improving resolution greatly. Resolution has also been improved by the use of lighter cyan and magenta inks, colors that appear smaller to us, and the ability of printers to spray different drop sizes [source: Mitchell]. Common default resolutions for inkjet printers are 300 to 600 dpi, with higher resolutions possible in a lot of printers, some going into thousands of dots per inch.

The earliest desktop laser printers (including that first HP LaserJet) printed at 300 dpi resolution. Common laser printer resolutions today are 1200 or 2400 dpi, with some lower-end models printing at 300 or 600 dpi. All are perfectly adequate for printing most documents, with dpis in those ranges not being terribly discernible from one another to the naked eye. Dpi does make a noticeable difference with photo printing.

With inkjet printers, the ink usually dries quickly, but in some cases the wet ink may need a little time to dry, so you can smudge it if you handle a newly printed page. With laser printers, the ink is fused to the paper before it exits the machine and does not smudge. The type of paper also makes a difference. Ink bleeds and spreads out on paper if it's too porous. Brighter white 24-pound paper is usually recommended for inkjets, rather than lighter 20-pound paper used for copiers and laser printers. Special photo paper is advisable for printing photographs.

The ink itself can affect print quality as well. Dye-based inks (which are soluble in water or other solvents) are better for blending colors and are therefore best for photos, but they may result in lines that are less sharp. Pigment-based inks (with insoluble pigment particles suspended in liquid) tend to result in sharper lines, so they're better for text, logos and other simple graphics. Indecisive? It's possible to find printers that let you swap cartridges to the type of ink you need.

The Price of Printer Ink

When you buy ink for your printer, part of what you’re paying for is the research that creates better ink.
When you buy ink for your printer, part of what you’re paying for is the research that creates better ink.
© HasseChr/iStockphoto

In 2013, Consumer Reports found that inkjet ink costs anywhere from around $13 to around $75 per ounce (or $1,664 to $9,600 per gallon), in many cases more costly than expensive champagne or perfume. It's sometimes cited as the most expensive liquid on earth, but that's just not true. Scorpion venom apparently has that distinction, at more than $30 million per gallon [sources: Venom SA, The Wall Street Journal]. But since consumer ink isn't purchased by the gallon, these comparisons are a little dramatic. And part of your consumer dollar is going to developing the ink technology of tomorrow.

According to HP executives, much of the cost of print cartridges has to do with research and development costs. Around 2010, they reportedly spent roughly a billion dollars annually on ink R&D, and it takes several years to develop a new ink. The ink has to be chemically formulated to remain homogenous, withstand high heat and the pressure of being pushed through a tiny nozzle at high speed, stick to the paper and dry quickly [sources: Ilett, Mitchell, Wood].

Some of the ink, however, doesn't make it to the printed page, instead being used for maintenance like printer head cleaning after the printer has sat idle for a while. Consumer Reports found that some models even lost more than half their ink to maintenance, although others had much lower ink loss. They suggest keeping the printer on most of the time, since they don't use much energy and some printers go into a long maintenance mode every time the printer is turned on. They also suggest using the lowest resolution necessary for your purposes and avoiding printing a lot of large photos high-quality photos [source: Consumer Reports]. If you don't use your printer for a while, the ink can dry and gum up the nozzles, either resulting in bad prints or rendering the cartridges useless and requiring replacement, so turning off and on or otherwise occasionally instigating maintenance is advisable.

You can also save money over time by shopping around for the right printer. Printers that use a tri-color cartridge that includes all three colors (cyan, magenta and yellow) tend to have higher ink replacement costs and waste ink because you have to replace the whole color cartridge every time one color runs out. They either print badly or the printer stops working until the cartridge is replaced. A laser printer, especially a monochrome one, could save you money if it meets your purposes. Laser cartridges might be a bit more expensive at time of purchase, but they tend to print a lot more pages and might be cheaper over time. Since toner is powdered, and there are no nozzles, the cartridges can also sit for a long time and still function, and they don't use toner for cleaning and maintenance functions. Color toner can be quite expensive, though, so inkjet printers might still be the go-to choice for home printing if you want color printing capabilities.

The expense of printer ink has spawned businesses dedicated to refilling printer cartridges with ink, or selling lower cost third-party rebuilt cartridges. You can also buy kits to refill them yourself, which you generally do by making a hole in an existing ink cartridge, inserting the special printer ink with a syringe and plugging the hole. In some cases these actions void your printer's warranty. The quality of off-brand replacement ink also varies. The print heads and other hardware on cartridges can also wear out from overuse, so refilled cartridges can't be used forever — they'll have to be replaced eventually.

Printer manufacturers have taken various steps to make their cartridges the more likely purchase. Some printers have encrypted microchips and other embedded technology to recognize their own cartridges and prevent off-brand cartridges from working. Some printer companies have started selling more expensive printers with built-in refillable ink tanks that should save the consumer money in the long run. And HP has taken to offering a monthly cartridge replacement service that varies from $2.99 to $9.99 per month depending on your expected usage.

The Future of Printing

Even if the home printing market shrinks, we’ll still continue to rely on printed packaging in our everyday lives.
Even if the home printing market shrinks, we’ll still continue to rely on printed packaging in our everyday lives.
© lovleah/iStockphoto

It's a little hard to find data on the percentage of households that own printers these days, but they're a pretty common peripheral for use with home computers, and they were especially useful before we could easily transfer digital documents. Around 2002, printer manufacturers were reportedly selling about $19 billion a year in ink cartridges alone, if that's any indication of their past popularity [source: The Economist]. But there have been some signs of decline. According to an analyst at the Photizo Group market research firm in 2012, sales of multifunction inkjet printers in North America reportedly dropped by 12 percent, and the drop was expected to continue. The number of pages printed on home printers has also dropped 15 percent since 2009 [source: Wood].

This might be because ink on paper is becoming somewhat old fashioned. Individuals, companies and public entities are moving to digitized forms, reports and communications. We can show event tickets and airline boarding passes on our cell phones instead of receiving them by mail or printing them out at home. We can store and share documents and photos in the cloud or via email rather than having to send them to share physical copies. We can sign documents using e-signatures, pay bills and file taxes online, and have purchase receipts emailed to us. We increasingly read e-books on our phones, tablets, computers and even on e-readers that mimic the look of paper and ink with technologies like e-ink. And we can use GPS instead of printing maps for trips. If digitization trends continue, further decreases in printer use will likely follow.

Printing technologies are, however, leading to some exciting new innovation. Researchers are working on conductive inkjet ink to print circuits, sensors, antenna and other hardware components onto paper, textiles and more. Some are even looking into inkjet printing DNA onto a substrate for use in biomedical studies. And outside of the lab, 3-D printers allow us to effectively print solid three-dimensional objects using plastics and other materials. There are now even 3-D printers that print food.

And good old printing ink is unlikely to disappear anytime in the near future. Some of us like to receive paper bills and receipts and print out backups of documents for safekeeping in case our technology fails. And it will be a long time before we digitize product packaging.

Author's Note: How Printer Ink Works

I remember using a daisy-wheel printer back in high school and being terrified I was going to wake the entire house up anytime I had a late-night printing session for a paper due the next morning. Inkjet and laser printers were certainly a godsend for their speed and noise-level. They also allowed us to start adding fancy graphics and color to complement all our papers and reports.

But there are some hassles, like those late-night runs to the store for a cartridge. Yes, it's my fault for putting off printing until the wee hours of the morning and for not heeding the warning signs of a cartridge running low. Until recently, I also gravitated toward cheaper printers that were ink hogs. Researching this article reinforced the idea that it's wise to invest in a printer with lower per-page costs, whether inkjet, laser or any future printing technology.

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