Grades 3–5 · Everyday Life
Why can erasable pen ink disappear and return?
Some erasable pens seem to remove their writing without leaving the crumbs made by a pencil eraser. In a thermochromic pen, the surprising change is mainly in the ink’s visible color. Thermochromic means that color responds to temperature.
In the diagramDisappearing color is not disappearing inkOne reversible thermochromic ink systemColored state before warmingMUSEUMColor systeminside capsulesSame paper and inkThe colored mark is visible; ink remains on the page.
Tiny capsules in this ink contain a color-forming system. Its ingredients include a dye, a color developer and a component that sets its temperature response. Warming can change how that system interacts, making a colored mark become nearly colorless. The ink has not simply been scraped away.
Sufficient cooling can restore the colored state. The temperature needed to bring color back can differ from the temperature that made it disappear, so the mark’s appearance depends on its recent thermal history. This is why an apparently blank area may still contain ink. The drawing follows one reversible ink system, not every product sold as an erasable pen.
About this explanation
Starting knowledge: Understands warmer and cooler and that a substance can change appearance without leaving its location.
Sources
- Pilot Pen Australia — Erase and Rewrite: Your Complete Guide to Erasable Pens
- Pilot Corporation of Europe — How do FriXion products work?