Rainbow Codes

Did you know…

Spies aren’t the only ones who use secret codes to send messages to one another…. the military and businesses use them too!

Today’s Activity: Made a Rainbow Decoder

You will need: Pencils – colored and regular, lined paper, plastic wrap, permanent red marker, an old business card, scissors or cutting tool (use a cutting board too), ruler, and glue

Step 1: Make a decoder

To make the decoder, you will need: clear wrap, permanent red marker, an old business card, a cutting tool, ruler, pencil, and glue.

– Use your pencil and ruler to measure a rectangle in the middle of the business card that is 1 1/2″ long x 1″ wide. Cut the rectangle out to form a window in the middle of the card.

– Color a 3” x 3“ area of the clear wrap with red permanent marker. When the marker dries, cut a 2″ x 1 1/2″ piece of the colored clear wrap out and glue it to the outer edges of the window of the business card. While your glue is drying, write your secret message.

Tip: You can also use a clear red file divider to decode messages. These are available in the dollar store.

Step 2: Write your secret message
– Decide what your message is going to be and write it on a scrap piece of paper if you want. For this example we’ll use:  DECODING IS FUN!

Next, figure out how many letters are in your message. Our example code has 13 letters, so in order to throw off the casual observer, we will make 35-45 dashes with a pencil so that extra letters can be added in different colors.

Example:  __ __ __ __ __ __ __ __ __ ….(one dash for each letter you are going to use)

– Write your code.  Alternate the colors by writing one letter in blue and the next in purple pencil. As you do this, skip a dash here and there but be sure to keep all the letters of your code in order.

__ __ D __ E __ __ C __ __ __O __ __ D __ __ I __ __ N __ G __ __ __I__  __ S __ __ __ __ F__ U__ __ N!

– Once your code is completely written out, fill in the blank dashes with random letters in a variety of colors. Here’s a finished example:


Notice how it resembles a rainbow?
Experiment to see what colors can and can not be used with your decoder window.

Step 3: Give your message to someone to decode

 – Give the coded message and decoder window to someone else to figure out. As they run the clear red plastic over the letters, all the unnecessary letters will “disappear” and your message with be revealed!

Question of the day:

Why did all but the dark blue and purple letters “disappear”?

Learn more:

Exploratorium: Secret Language
Learn more about codes and ciphers

How Stuff Works: How Light Works
Learn how light works

The Magic School Bus Makes a Rainbow
Activities you can do with color

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