Despite the fact that you’re likely reading this article on a screen, paper consumption in the United States for the last 20 years has increased from 92 million tons to 208 million -- a growth of 126%.

Given the environmental toll, Carl Yee wanted to print paper without the guilt.

After time spent engineering car doors for Saturn and designing medical devices for Boston Scientific, Yee thought of an idea that he couldn’t believe hadn’t been patented before: Disappearing ink for printers.

The former engineer then spent time in his San Diego garage formulating what he described as a purposefully “lousy ink” – one that slowly fades after being printed. The gradual disappearance of the ink allows the paper to be used again and again.

How does the invisible innovation work exactly?

Compatible with today’s printer technologies, the ink itself is essentially an acid-base, or pH, indicator. The ink contains a base to raise the pH and make the ink’s initial color a blue-red hue when printed.

Thymolphthalein, the indicator currently used in one version of the formulations, is blue when the pH is high and colorless when the pH is neutral or low.

Upon printing, the air’s carbon dioxide reacts with water in the ink to form carbonic acid. The carbonic acid then reacts with the base in the ink to produce carbonates and water.

As the base is consumed by these reactions, the acid-base indicator becomes colorless and thus the ink becomes invisible.

Yee’s idea, an honorable mention in the 2017 ‘Create the Future’ Design Contest, is set to be released in 2019. The inventor spoke with Tech Briefs about how he envisions his “PaperSaver” technology being used – and how the ink can help alleviate some of that “print guilt.”

Tech Briefs: How does your ink differ from regular ink in printers?

Carl Yee: The difference with this PaperSaver ink is it was not engineered to last forever. It was designed to be really lousy ink that fades. But it doesn't just fade and become yellow; it completely disappears. Conventional ink was designed to be smudge-proof and last forever. This ink was intended to allow the paper to be used over and over again.

Tech Briefs: How did this idea come about?

Yee: It really came about as I was thinking about the environmental impacts of printing. There were times where I did end up printing, and I always felt guilty about it. I thought, "You know, this is kind of silly, because I print these things out, and then I go ahead and recycle them." So, it seemed to me, if you could just reuse the paper, that would make the most sense. I figured that the simplest thing would be if the ink just disappeared.

I figured, “That seems like an obvious idea; somebody must already be selling that,” and I looked all over trying to buy some. Turns out nobody had created that yet, and I dug a little deeper and found out that nobody had patented that idea either.

So, I have no background in this particular area, but I decided, "What have I got to lose by trying to invent this?"

I bought some disappearing ink and put it in an ink jet printer. Of course, it did not work at all, but I think the fire had been lit, and I've kept working on it for many years. Now it's pretty much ready to go.

Tech Briefs: In what kinds of applications do you envision this ink being used?

Yee: It works best for people who have to print sometimes, but feel guilty about it. And, I think it works best in an application where you're printing several pages at once. If you're printing a twenty-page paper that you've written, and you correct some typos, and then you print it again to make sure that it's right – that's an ideal application, because you're going through a lot of paper.

In preparation for my speaking with you, I ended up printing out some notes, and I realized I would need them for the next hour or two, and then I would not need them again. So, I printed them out using the self-erasing ink.

When we're done, I'm just going to put these papers in a stack and forget about them, and probably about three weeks later they will be completely blank, indistinguishable from regular paper. I can put those back into a printer, I can make notes on them, I could print them again with self-erasing ink, or use regular laser/inkjet printing.

Tech Briefs: What will your paper look like after the ink erases?

Yee: The paper is going to look completely blank. You will not be able to tell, even with a magnifying glass, that this was not brand-new paper.

Tech Briefs: How much time does it take for the ink to fade?

Yee: The printing begins to fade immediately, and it's a gradual process. So, generally readability is good on the first day, decent on the second day, kind of marginal on the third day, but then it takes, depending on how dark the printing was, two to three weeks until it's completely blank.

Tech Briefs: Is there a way to engineer the technology to offer different fading times?

Yee: Yes, it is possible to engineer different versions that would disappear at different rates. Also: If you print darker, more ink is on it and it will last longer. If you print lighter, it will disappear faster.

Tech Briefs: Does the ink look like your standard ink that comes out of a printer?

Yee: No, it doesn't. It has sort of a violet magenta type color to it. And, there are a couple of reasons for that. One: it's a lot more achievable than black. Also, if it looked exactly the same as regular ink, there'd be a lot of confusion. You could print something out in a rush to take over to a meeting, get there, and realize "You know what? I used the wrong ink; this thing just disappeared on me." So, it's a very good way to have a visual cue, that this is something special.

Tech Briefs: Is there any new printer technology needed to use this product?

Yee: There's no new technology required for this ink. It uses any kind of paper that's available. I often use the cheapest paper that's around. It also doesn't require any kind of special printer. It's compatible with ink jet printers; there's no new hardware needed at all.

Tech Briefs: For how many print jobs can you use the same piece of paper?

Yee: It really depends on the wrinkling of the paper, because a wrinkled piece of paper will eventually jam up the print feed mechanisms. I went up to ten times in testing, and then realized, "You know, it's kind of silly to see if I can get fifty.” So, it's more or less indefinite.

Now, if you're going to print, say, a photograph, or graphics over text on reused paper, you will see a ghost image of what used to be on there before. However, if you're just printing text over it, that's not an issue, because the lines in text are so small.

Tech Briefs: What are your biggest challenges in encouraging use of this?

Yee: Paper has been a disposable resource. We're not used to reusing paper, so I think there's a mindset and behavior change required; that might be a challenge.

Tech Briefs: Have there been any funny or interesting reactions to your technology, given that it’s a kind of “invisible ink?”

Yee: Oh, yeah. There are a lot of jokes about printing out contracts where certain words disappear. People have been talking about, say, coupon validation. You might have something that's only good for a day, and then the code disappears, and you can't use it anymore. There are also possible security applications.

Tech Briefs: What is the release plan?

Yee: I'm planning to launch in 2019. Before that I want to do a little more testing, and some pilot usage as well. For example, I was speaking with a local law firm, and they're trying to go paperless, but not succeeding. I'll just give them a printer, and say "Here’s some ink, try this out, tell me what works for you, and what doesn't."