20.05.2025
The first time I got my hands on an ink eradicator, I like every other curious student used it for everything except its intended purpose. By the end of the day, I had more ink eraser on my hands than on my paper, wearing it like some sort of paint.
One thing that stuck with me though, was the smell. If you’ve ever gotten an ink eraser on your skin, you’ll remember it - slightly unpleasant. At the time, I never thought much about it. But now, 13 years later, I can finally put my finger on it. That smell? It’s something sulfurous, and I started wondering…what happens when you eradicate ink?
Autorin: Aysan Yilmaz
Ink, commonly used in everyday applications and particularly by children in primary schools, is formulated to be non-toxic. It consists of an aqueous solution of molecules that contain chromophores, which are responsible for its color, along with additives that optimize ink flow and stability. While the specific chromophores vary depending on the color, they all share a fundamental structural feature: a conjugated π-system.
Anthraquinone, Beta-Carotene, Sudan-I, and Crystal Violet are chromophores with conjugated π-systems. They absorb different wavelengths in the UV-VIS spectrum and we can detect the complementary color.
But what is a π-system? Molecules that contain an extensive π-system have alternating single and double bonds with sp2 hybridized carbons. If the system is large enough, it starts absorbing visible light due to electron excitations. The human eye seeds the wavelength of the light not absorbed by the chromophore, so it needs to be the complementary color. For a blue ink to be visible as blue, the molecule absorbs yellow-orange light. What is this ink eradicator? Ink eradicator pens disturb this conjugated system of the chromophores by nucleophilic addition. The respective wavelengths that get absorbed and reflected are no longer associated with the initial color of the ink.
Each company has its own formula for the composition of its optimal ink eradicator, but a good nucleophile generally does the job. This nucleophile attacks the central carbon in the ink and reacts with it. The result of this reaction is the discoloration due to the disrupted π-system. In the case of crystal violet, instead of one big conjugated system, we have three smaller ones. The pigment molecule changes its geometry from planar to a pyramidal geometry and our carbon becomes sp3 hybridized.
Ink eradicators work by disrupting the conjugated π-system with a nucleophilic addition. Here, the chromophore is one large conjugated system (blue) and reacts to a molecule containing three small conjugated systems (blue, red and green on the right) in a nucleophilic addition reaction. Thank you Silas for the ChemDraw!
At this point, we have enough knowledge to debunk its German name “Tintenkiller”: We do not “kill” the ink in the sense that we break the molecule apart, we change the compound to a colorless one. A common compound used for the discoloration of ink is sodium sulfite acting as a nucleophile - also explaining the smell.
In the chemistry laboratory, we tried to make our own ink eradicator to test it with some store-bought ink. Our ink eradicator consisted of sodium sulfite dissolved in water with some NaOH pellets dissolved in it. As soon as the ink came into contact with the ink eradicator, the color disappeared! Isn’t that cool?
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