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Write on a whiteboard, swipe once with a dry duster, and the ink is gone. Do the same with a permanent marker and it stays put. The two pens look alike and share most of their ingredients. The difference comes down to one extra ingredient in the ink and the kind of surface it lands on.
It uses ideas from class 11 chemistry: solvents, evaporation and the weak forces between molecules. (Ballpoint ink works on a different principle again; the story of how László Bíró built the ballpoint pen is a good companion read.)
Why do whiteboard markers wipe off?
Both kinds of marker contain water, preservatives, pigments and solvents, and the solvent is usually isopropanol, according to the Royal Society of Chemistry's Education in Chemistry explainer on whiteboard markers. When the solvent evaporates, it leaves a sticky ink resin that binds to the surface through van der Waals forces, the same RSC article explains.
In a dry-erase marker, the resin comes with silicone, which the RSC describes as a lubricant that prevents the ink from bonding with the surface. An ingredient that does this job is called a release agent.
The recipe is written out in US patent 6031023, a dry-erase ink composition filed by Milliken in 1997. It lists a colorant, a volatile solvent at 30 to 80% of the ink by weight, a binder resin at 8 to 20%, and a release agent at up to 12%, with 9% as the most preferred amount. The patent says these release agents facilitate the removal of the binder resin film from the writing surface. Its preferred release agent, bis(2-ethylhexyl) sebacate, is an oily ester rather than a silicone, so different inks can get the same slip from different molecules.
Why does permanent marker not wipe off?
Permanent marker keeps the resin and leaves out the release agent. The RSC explainer says permanent markers contain acrylic, which dries to a shiny finish and acts as a protective coating for the ink. With nothing slippery in between, the resin's grip on the board holds, and a dry duster cannot break it.
Alcohols such as isopropanol suit marker makers because they are volatile: they carry the colour out of the felt tip and then leave. Water, the solvent you know best, is far slower to go; see why water is such a good solvent for life for what makes it special.
Why does the board matter as much as the ink?
The board is half the trick. The same Milliken patent describes whiteboard surfaces as plastic, enamel, melamine or polypropylene, and says they are impermeable to moisture, so liquids do not easily adhere to them. The ink cannot soak in, so it dries as a thin film sitting on top.
Paper is the opposite: a mat of fibres that pulls liquid into its gaps. That wicking is the same effect that drives paper and thin-layer chromatography. Once ink is inside the fibres, a release agent has little to lift, which is why a dry-erase marker will not wipe cleanly off a notebook page.
How do you remove permanent marker from a whiteboard?
The stuck resin is held only by weak forces, so the fix is a solvent that dissolves it again.
Scribble over the stain with a dry-erase marker, then rub with a cloth. The RSC notes that because dry-erase pens contain isopropanol, this can help remove the stain.
If a mark remains, use a little alcohol on a cloth. Marker maker edding's advice on permanent marker on whiteboards lists ethanol, methylated spirit or isopropanol, and says to test an inconspicuous area first.
Finish with a damp cloth and let the board dry.
Use alcohol in a ventilated room, away from flames, and keep it out of reach of young children.
Try it: can you make a drawing float?
This experiment comes from a Science Buddies activity published by Scientific American. It shows the release agent at work.
On a plate or shallow tray with a smooth surface, draw a stick figure, a heart or a word with a dry-erase marker.
Let it dry for a couple of seconds.
Pour in just enough water to cover the drawing. Wait and watch the drawing lift and float.
Make a drawing on a second plate with a permanent marker and add water the same way.
The article explains that the oily silicone polymer in the dry-erase ink stops it attaching to the plate, so water slips underneath, and because the ink is lighter than water it floats. The acrylic resin in the permanent marker makes that drawing stick.
Then write down a prediction before each of these runs; if you were wrong, the gap shows you what to revise:
Draw on a paper plate. What happens to the ink, and why?
Leave a dry-erase drawing for a day before adding water. Does it still float?
If van der Waals forces or solvent polarity feel shaky, the Fermi Concept Library covers concepts across physics, chemistry, biology, mathematics and computing. For ideas that are easier to see than read, try the interactive simulations in the Fermi Simulation Lab.
