Someone trying to sell a baseball allegedly signed by Babe Ruth in the early 1920s, or pass off documents as older than they really are, is up against a serious foe: The United States Secret Service.

You might know that the Secret Service is on guard against counterfeit currency. You might not know, however, that it also keeps a one-of-a-kind International Ink Library with more than 11,400 specific writing ink fingerprints on hand. The ink library handles a variety of cases, from threat letters — the Secret Service protects not only the President but also other high-profile government officials — and ransom letters, baseballs, and phony documents where someone is "trying to obscure the truth in some way," says Joseph Stephens, ink library document analyst.

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Want to cover up insider trading by adding information to a stock worksheet after the fact? Then you should have used the same exact pen as the original, since the FBI and the Secret Service have teamed up to crack those kinds of cases simply through ink analysis. Anytime you write something down, it's more than your handwriting that can give you away.

Want to cover up insider trading by adding information to a stock worksheet after the fact?

Investigating ink

This library was created in the late 1960s at the Bureau of Alcohol, Tobacco, and Firearms until it grew and moved to the Secret Service and its Washington, D.C. forensic services lab in 1988. It contains inks dating to the 1920s, pens Secret Service agents collected on worldwide travels, and annually updated samples solicited from ink manufacturers.

With all this data, the Secret Service can do what's called static ink dating to support a variety of criminal investigations. With static ink dating, analysts can determine when an ink was first made available to the public, says Julia Barker, ink library document analyst. This is the most common type of investigative request the library receives. (It takes requests not only from the Secret Service but also law enforcement agencies across the nation, and occasionally worldwide.) Consider the case of the alleged Bath Ruth baseball — static ink dating can investigate the ink and determine if it was even available during the right timeframe.

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The library's analysts walk through three different types of examinations. The first — the physical tests — simply take stock of the type and color of ink. The second tests go beyond the visual‑investigators might examine the document in ultraviolet and infrared light to see how the ink reacts. "Looking outside the visible spectrum, some of the inks will disappear and come transparent," Stephens says. "Other inks absorb. We can determine the number and type of inks to categorize inks into classes."

The final leveling of testing, which happens at the chemical level, involves what's called thin layer chromatography. This process separates the ink on a thinly coated piece of paper. Using solvents, Secret Service analysts can separate individual bands of color, or dyes. Black ink is never just black, after all. It may be a mix of multiple purple and yellow dyes, or some other combination, so don't believe your naked eye.

Black ink is never just black, after all

"The chemistry of ink is such that it is rare that the color the human eye perceives is the color the dye is that is used," Stephens says. By comparing the bands to the over 11,400 inks in the library, the analysts can pinpoint the manufacturers creating the specific ink.

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The chase doesn't end there, because ink doesn't stand alone. To get the full picture, investigators also need to take into account the paper. They take small punches of the paper to determine if any color from the paper shows up in the ink sample. They also check whether the paper is coated. If so, then the ink might sit on top of the paper. But with an uncoated piece, such as typical computer paper, ink seeps right in, Barker says. Understanding the type of paper not only gives investigators another clue, but also tells them more about the properties of the ink. And while they're already looking at paper and ink, analysts spend time inspecting the document as a whole, whether for watermarks, brighteners, branding on the paper, toner or defects that can help trace the machine that printed the document.

Beyond the page

The International Ink Library is in the midst of moving to a fully digital catalog, which will exponentially speed up the effort to match inks. Having the entire library digital also opens up the possibility of sharing ink information worldwide.

Testing is getting better, too. The group is researching it calls dynamic ink dating — an attempt to measure the precise dryness level of an ink, which can help to pinpoint the date it was applied. This is done through gas chromatography-mass spectrometry:

While the research aims to expand the reach of the world's largest ink library, the ink fingerprinting continues, whether for a Babe Ruth baseball, a fraud case, or even a ransom note. Because black ink is far more than it first appears.