Science Projects > Chemistry Projects > How To Make Invisible Inks 

How To Make Invisible Inks

Invisible inks are also called sympathetic inks and can be made with many different substances. Sometimes they appear when you heat them up; other times another chemical can reveal them. Get creative and see how many kinds of invisible ink you can find.

(NOTE: Some of the chemicals used in this project can be hazardous if misused. Use caution when working with chemicals! Read the information on the chemical label before you start, and always wear protective safety equipment such as goggles, gloves, and aprons. Adult supervision required.)

What You Need:

  • Ink type 1 –  lemon juice, grapefruit juice, vinegar, milk, onion juice
  • Ink type 2 – cobalt chloride
  • Ink type 3 – phenolphthalein, Windex
  • Q-tips or paintbrush

What You Do:

1. Choose a liquid like lemon juice to use as ink. Write a message on a piece of white paper using a paintbrush or q-tip, dipping in the ink frequently. Let the message dry. Turn on the toaster and carefully hold your paper over it. The heat will make your secret writing appear!

2. Some sympathetic inks appear and disappear again based on humidity. To try one of these, make a solution of 1/8 teaspoon cobalt chloride and 1/2 cup water. After writing your message and letting it dry, heat the paper to see your message appear in blue. Now hold the paper face down over a pan of steaming water. The steam will cause the writing to disappear. If you reheat it (evaporating all the water) the writing will appear again.

3. Other sympathetic inks work because of acid-base reactions. Use phenolphthalein solution to write a message on a piece of paper and let it dry. After it is dry, spray it with some Windex. Phenolphthalein is a pH indicator that is pink in the presence of bases. Since Windex is a base, it causes your phenolphthalein writing to appear.

What other sympathetic inks can you find? Which kind shows up best? Which kind lasts longest?

Chemistry

Welcome! Read other Chemistry articles or explore the rest of the Resource Center, which consists of hundreds of free science articles!

Shop for Chemistry Supplies!

Home Science tools offers a wide variety of Chemistry products and kits. Find affordable beakers, test tubes, chemicals, kits, and everything else you need for lab experiments.

Related Articles

Thanksgiving Family Genetics Activity

Thanksgiving Family Genetics Activity

This Turkey Family Genetics activity is a fun way to teach your student about inheriting different traits and spark a lively conversation about why we look the way that we do.

Homeschool Science Dissection Kits

Homeschool Science Dissection Kits

Homeschool science dissection kits are an important part of a homeschool science curriculum. But, many parents often get caught up in thinking that high school science labs need to be hard. Not so! There are many homeschool science dissection kits that are available...

10 Science Experiments You Want To Do This Year

10 Science Experiments You Want To Do This Year

Science experiments are one of the most fun things you will get to do in your homeschool or classroom! You’re not only learning and applying knowledge — you’re also having fun! I've put together some really fun and easy science experiments for you and your family to...

Modeling Ecosystem Food Webs with Owl Pellet Dissection

Modeling Ecosystem Food Webs with Owl Pellet Dissection

Grade Range: Adaptable for Grades 3 - 8. Overview: Learn about food webs by dissecting owl pellets. What You Need: Owl Pellet Dissection Kit Activity Objective: Draw and understand a food web based on what is observed in an owl pellet. Safety...

should I learn computer coding