Science Experiment for Ink Lovers: Chromatography

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What color is your fountain pen ink? Black? Brown? Burgundy? That may be what color it appears to be, but the chances are good that it’s really not that color. I’m not suggesting that you’re color blind, not at all. What I’m saying is that ink colors are an example of the maxim, “Things are not always as they seem.” Read on for an explanation.

Color sampleWith a few exceptions such as iron gall ink and nanoparticle inks (e.g., Platinum Carbon Black), modern fountain pen inks derive their colors from aniline dyes. In this article, I will discuss only dye-based inks. Aniline dyes came into being in 1856, when a chemistry student named William Henry Perkin accidentally discovered mauveine (aniline purple) during an attempt to synthesize quinine. Perkin patented his discovery and within a year had opened a commercial dye works at Greenford, London, England. He called his dye Tyrian purple, after an ancient natural dye made from a secretion of certain snails in the Murex family. Tyrian purple is also known as Roman purple; it is the reddish purple color that the Romans used as trim on senators' togas and for other ceremonial purposes. The round swatch to the right is as close to the color of Tyrian purple as I can generate in a Web page.

Because the chemistry of aniline dyes does not permit an extensive range of colors, the dyes come in a relatively restricted selection of basic colors. To produce inks in colors other than those hues, ink makers must mix various basic colors to get the hues they want. Because there’s no true black aniline dye, for example, black fountain pen inks are always made up of multiple dyes unless the colorant is nanoparticulate carbon, a pigment rather than a dye. The left-hand image below is a chromatograph of Waterman Intense Black (which actually isn't very intense at all). The blue dye reflects blue light and absorbs almost everything else, while the yellow dye reflects yellow light and absorbs almost everything else. Because blue and yellow are complementary colors on the emissive color wheel, almost no light is reflected from this mixture, and the result is that the ink looks black. The right-hand image below shows Aurora Black, in which there is still a yellow, but where the blue is replaced with a very deep purple that is much darker than Waterman’s blue, with the result that Aurora Black is a more intense black than Waterman.

Ink chromatograph Ink chromatograph

The next two images are chromatographs of Waterman Absolute Brown (formerly Havana) and Waterman Mysterious Blue (formerly Blue-Black).

Ink chromatograph Ink chromatograph

To get that perfect brown with the slightest cast of red for Absolute Brown, Waterman started with a reddish dye (the color of burnt sienna) and added to it a little cyan and a tinier amount of yellow. (The yellow is barely perceptible right at the point where the reddish and cyan dyes separate.) The cyan darkens the mixture in the same way that blue and yellow make black, which is darker than either of them, and the yellow keeps the color from being too cold. For Mysterious Blue, the mixture is indigo (blue), yellow, and cyan. This ink goes on clear blue and dries over a period of days, as the indigo fades, to leave the characteristic greenish teal color that engendered the “Mysterious” name.

The final two images are chromatographs of Diamine Syrah and Diamine Woodland Green.

Ink chromatograph Ink chromatograph

The central area of the Syrah should look familiar. It's mauveine, the first aniline dye to be discovered. The darker areas in this chromatograph appear to be a dark brown dye, and the faded, areas at the top and bottom of the blot appear to be something in the orange range. In the Woodland Green, the central area is a slightly yellowish medium green, while the periphery is cyan. This combination produces a green that seems to have no bluish or yellowish cast.

What’s the point? If you’re like many ink lovers I know, you enjoy mixing your own ink colors, but they don’t always come out the way you expect them to. Knowing what colors are actually in an ink you’re working with can help you to reason out what will happen when you mix it with other inks whose constituent colors you also know. But even if you don’t plan to mix your own colors, just seeing what goes into your favorite ink is fun.

All right, then, how do you make your own chromatographs? Use a very simple technique known as paper (ink blot) chromatography. Paper chromatography is the poor man's version of thin layer chromatography, a precision laboratory technique used in many branches of science including forensics, where one of its uses is to determine whether two samples of writing were made using the same ink.

To perform your own paper chromatography, lay a fresh paper towel on a nonabsorbent surface. (A sheet of clean glass is ideal, but a truly clean cookie sheet will also work well.) Put a drop of ink on the paper towel and add five drops of plain water, dropping each one as near to the center of the blot as you can manage. The liquid will spread out as it bleeds through the paper, and the various dyes that were used to make up the color will spread at different rates. Let the blot dry, and see what you get. To get the most uniform blots, use cheap single-layer paper towels; quilted double-layer towels will produce blots that look more like plots of the Mandelbrot set in mathematics, with irregular shapes and uneven color spread.


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