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How to Make Disappearing Ink


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Make Disappearing Ink
This is the chemical structure of thymolphthalein.

This is the chemical structure of thymolphthalein.

Ben Mills/PD
Here's how to make your own disappearing ink:


  1. Dissolve the thymolphthalein (or phenolphthalein) in the ethyl alcohol.
  2. Stir in 90 ml of water (will produce a milky solution).
  3. Add sodium hydroxide solution dropwise until the solution turns a dark blue or red (might take slightly more or less than the number of drops stated in the Materials section).
  4. Test the ink by applying it to fabric (cotton tee-shirt material or a table cloth works well). Paper allows less interaction with air, so the color change reaction takes more time.
  5. In a few seconds, the 'stain' will disappear. The pH of the ink solution is 10-11, but after exposure to air will drop to 5-6. The damp spot will eventually dry. A white residue may be visible on dark fabrics. The residue will rinse out in the wash.
  6. If you brush over the spot with a cotton ball that has been dampened in ammonia the color will return. Similarly, the color will vanish more quickly if you apply a cotton ball dampened with vinegar or if you blow on the spot to improve air circulation.
  7. Leftover ink may be stored in a sealed container. All of the materials may be safely poured down the drain.

Disappearing Ink Safety


  • Never spray disappearing ink into a person's face. Particularly avoid getting the solution in the eyes.
  • Preparing/handling the sodium hydroxide (lye) solution requires adult supervision, as the base is caustic. In case of skin contact, immediately rinse well with water.

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