OPERATION: Invisible Ink

OPERATION: Invisible Ink

Materials Needed:

  • Paper
  • Pen
  • Writing source (cotton swab, paintbrush, feather, finger)
  • Organic liquid (lemon/apple/orange juice, milk, vinegar)
  • Heat source (light bulb, iron, oven, open flame) **Have parental supervision**


The Book of Daniel tells us an interesting story about how God revealed His plan to an evil king. King Belshazzar was having a party with his friends and he wanted to show off the spoils of his dad’s conquest of the Israelites. He ordered for the vessels that were taken from the temple to be used to eat and drink from. He witnessed a Man’s hand writing a coded message on the wall that none of his men could interpret, except the prophet Daniel. It spelled the end for King Belshazzar. Secret messages have been used for many years and many purposes, like the military and government, as well as for fun between kids. Today, we will learn how to write with invisible ink using common household items.


  • On a piece of paper, write a normal looking letter that would not make anyone think there is a secret message within the letter
  • Obtain your “secret ink”(lemon juice, milk, etc) in a small container
  • Use a paintbrush, cotton swab, or your finger to write a secret message with “invisible ink” on your letter
  • Allow the paper to dry for 30 minutes
  • When you are ready to read the invisible message, hold the paper over a light bulb, or other heat source (If using an iron or open flame, have parental supervision)
  • The heat will cause the writing to darken to a light brown color and your message will become visible. The writing turns brown because the organic material burns before the paper
  • Experiment with different juices and writing instruments to get your favorite combination
  • Send messages to your fellow Project22Six Operatives about “CONFIDENTIAL” information on meeting places and times. Have fun and be creative!!


  • Which juice was the best to read after it was heated?
  • What was your favorite writing material?
  • Why do you think that the “invisible ink” turned brown and not another color?

Life Application:

For some people, the Bible seems like a book that was written in a secret code. For the believer, God has given him understanding, which comes from the Holy Spirit. Jesus spoke to His disciples, saying “To you it has been given to know the mystery of the Kingdom of God; but to those who are outside, all things come in parables.” (Mark 4:11)

  • Are there things in the Bible that are a mystery to you? If so, what are they? Pray that God would reveal His Word to you as you read the Bible and give you understanding.
  • Look up Matthew 13:1-9 The Parable of the Soils. What does this story that Jesus told mean to you?
  • Now, read Matthew 13:18-23 and hear how Jesus explains this parable to His disciples. What type of soil is your heart in?
  • What can you do to keep the soil of your heart soft towards God?

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