Invisible Ink Demonstration

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In this chemistry demonstration, learners will discover that phenolphthalein is a chemical that displays different colors depending on the acidity or basicity of the environment. Learners will be surprised to see a "secret message" appear in bright pink ink when it is sprayed with Windex containing ammonia (a base). They compare this to what happens when the message is sprayed with Windex containing acetic acid (nothing!).

Quick Guide

Preparation Time:
5 to 10 minutes

Learning Time:
Under 5 minutes

Estimated Materials Cost:
$5 - $10 per group of students

Age Range:
Ages 6 - 18

Resource Types:
Activity, Demonstration, Experiment/Lab Activity


Materials List (per group of students)

  • phenolphthalein solution
  • cotton swab or artist's paint brush
  • white typing paper or paper towel, roll
  • 100 mL beaker, glass or plastic cup
  • ammonia or Windex spray with ammonia
  • acetic acid or vinegar


  • Physical Sciences
    • Chemistry
      • Acids and Bases
  • The Nature of Science
    • The Scientific Process
      • Conducting Investigations

Informal Categories

  • Crime Science


To use this activity, learners need to:

  • see
  • see color

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access with registration