About Chemical Innovation - Subscription Information
September 2001
Vol. 31, No. 9, p IBC.
The Last Word

Table of Contents

Debra A. Schwartz

Just for the gel of it

Opening art
Corbis Corp

If you’re thinking of sketching a tattoo onto your hide or just want to put your everlasting signature on a trust fund, gel inks offer your kind of flexibility.

The bad news is that a gel pen fills only one-eighth as many pages as a standard ballpoint pen. But these pens are doubling manufacturers’ profits because the write is smooth and fast. I like to think it’s also because the ink is nontoxic and ecologically friendly. Moreover, the inks wash off skin with soap and water, and the blues and blacks hold archival status because they don’t fade on paper.

Economically speaking, even though it takes eight disposable gel pens to write as many pages as a standard ballpoint, in the long run they reduce hazardous waste cleanup. These wild and crazy metallic, pastel, sparkle, and regular color inks are 80% water, in contrast to ballpoint inks, which rely on solvents—mainly phenoxyethanol and benzyl alcohol—to carry their colors.

The colors in gel inks typically come from copper phthalocyanine pigments and iron oxides. Additives to gel inks are mostly biopolymers, such as xanthan and tragacanth gums, and some types of polyacrylate thickeners, according to Bruce Gindelberger, vice president of R&D for National Ink Inc. (Santee, CA). If you have leftover gel ink that is eventually buried in the ground, there wouldn’t be a lot of organic chemicals to leach into the groundwater, he added.

The sparkles in gel pens typically are powdered aluminum, but their shapes and the amounts used vary from one company to another, according to Peter Ouyang, vice president of product development for Sakura of America (Hayward, CA), whose parent company, Sakura Color Products Corp. (Osaka, Japan), makes Gelly Roll pens and was the company that invented gel ink in 1984. However, Sakura uses cosmetic-grade ground glass in its Stardust pens. “You get a much better sparkle from glass,” Ouyang said.

Despite their high water content, gels are not transparent like conventional inks. Gel inks use pigments suspended in a water-soluble polymer matrix, which makes them opaque. Other writing inks are transparent because they use dyes—not pigments—in solution. This applies to paste ink for ballpoint pens and liquid inks for fountain pens.

The suspended pigments give gel ink its permanence, but they also cause problems for the U.S. Internal Revenue Service and Secret Service, the two government agencies that analyze inks. A special resource collection, started in 1968 by the Bureau of Alcohol, Tobacco, and Firearms when it was still part of the IRS, was turned over to the Secret Service in 1988 and named the International Ink Library. It collects inks from manufacturers annually.

Until the gel inks arrived, it was possible to differentiate inks by their dye combinations using thin-layer chromatography (TLC), which separates organic compounds. Gindelberger explained that forensic scientists can use TLC to check the combination of dyes present in regular inks because the dyes migrate. But the pigments in gel inks don’t migrate, so there is no distinctive pattern. They all look like carbon black.

A conventional black ink contains two or more dyes. When the ink is exposed to a solvent system, forensic scientists can see the characteristic pattern of the colors, and hence identify the manufacturer—and possibly the year of manufacture, because companies usually modify their formulas a little every year. But because gel ink pigments are insoluble, scientists must use different means to obtain this information.

“I’m certain we’ll see gel inks in future casework because of their increase in popularity. We’ll need to know how to distinguish among them,” said Larry Olson, a document analyst and ink chemist with the IRS.

Olson has found that illumination with IR and UV radiation is somewhat useful for classifying some gel inks. “We dissolved the pigments and recrystallized them, and it looked like—in the case of the blue and green copper phthalocyanine pigments—we could differentiate them by their morphology, but we had limited success,” Olson said, noting that recent articles have also reported success with Raman spectrometry.

Most gel pens are the inexpensive “stick” type. However, some of us must have a retractable pen because we lose the caps and the ink gets where we don’t want it. For such people, Cross Pen recently began offering the first retractable, refillable pen that uses gel ink. For a modest $25, and refills that cost $3.30, we can sign our IRS forms in electron red, galaxy green, and pulsar purple.

Debra A. Schwartz is a freelance writer and editor in the Washington, DC, area (debinmld@aol.com).

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