On the Board at Washington Global:

How does a dry erase marker remove permanent marker?

by Ms. Kimberly Fuller

As a teacher, there have been so many times my class, and I have been fully engaged in the teaching process. All of a sudden I go to write down a wonderful thought from a knowledgeable student on the whiteboard when unexpectedly my heart drops! I can't believe I just wrote on the board with a permanent marker. What am I going to do? HELP!!


Let’s start with the four core ingredients used in the formulation of ink: water, additives, solvent, and preservatives. The solvent varies in each type of marker while the other ingredients remain fixed. Both permanent and dry erase markers contain a dye or pigment in an organic solvent. The main difference is in the added polymer. Permanent markers use toluene and xylene in their solvent which gives the markers their ability to leave long-lasting marks. Dry erase markers use the same solvent as permanent markers but add a different polymer which is illustrated below.


The permanent marker uses a polymer, like an acrylate, that joins the coloring agent to the surface, fundamentally through van der Waals forces, and is not water soluble. The colorant is also more likely to be pigmented which usually have lower water solubility than dyes. Initially, the solvent in permanent markers tended to be xylene, but because of concerns over possible toxicity (especially as markers were used more and more in schools) many manufacturers switched to the less toxic alcohols, like isopropanol (a/k/a, rubbing alcohol) often along with co-solvents like 2-butoxyethanol and glycols.


Images from Happy Atoms

But how does a dry erase marker remove permanent markers? Dry erase markers contain a chemical solvent made of alcohol, which happens to be an excellent solvent for the pigments in permanent markers. So picture this, when the teacher writes with a permanent marker, the marker adheres to the board. When he or she traces over it with a dry erase marker, they're adding pigment and solvent to the board. The solvent dissolves the permanent marker underneath and allows each part - dry-erase pigment, permanent marker ink, and the solvent - to be wiped away. Voila Magic!


It may be confusing to wrap your head around the fact that tracing on top of a permanent marker is the best way to remove it, but useful coincidences like this happen every day. When you’re able to understand and appreciate the science that’s going on behind the scenes, it all becomes a bit more clear–and sometimes clean.



Vocabulary:


  • Additives - a substance added to something in small quantities, typically to improve or preserve it
  • Solvent - the substance doing the dissolving; a substance that dissolves a solute (a chemically distinct liquid, solid or gas), resulting in a solution
  • Preservatives - a substance used to preserve foodstuffs, wood, or other materials against decay
  • Organic solvent - a chemical class of compound; they share a common structure (at least 1 carbon atom and 1 hydrogen atom) and have a lower density than water, which means they are lighter than and will form a layer on top of water.
  • Polymer - a substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together
  • Van der Waals forces - a general term used to define the attraction of intermolecular forces between molecules. There are two kinds of Van der Waals forces: weak London Dispersion Forces and stronger dipole-dipole forces.
  • Solubility - relative capability of being dissolved
  • Toxicity - the quality of being toxic or poisonous