Ever dreamed of being a secret agent? Well, you're in luck! Today, we're going to uncover some secrets of invisible ink. It's simpler than you think, and all you need are a few household items.
What you'll need:
1-2 Tb Baking soda
Water
1-2 tsp of Turmeric, if you don’t already have this spice then recommend purchasing a small amount from bulk section of your local grocery store
Can also use fresh turmeric root, a 2 inch long piece is less than 25 cents!
Approx. ¼ cup hand sanitizer or Rubbing alcohol (70% isopropyl alcohol), either will work
A color changing compound in turmeric is extracted into the alcohol and will turn it yellow, undissolved turmeric will remain on bottom (do not use this part of mixture). This solution is shelf stable and will keep its ability to change color for several months.
You can use water instead of alcohol, but the color won’t be as bright and will degrade over time, losing its ability to change color.
Cotton swabs or fine paintbrush
White paper
2 cups, at least one should be glass or plastic that you don’t mind getting stained by turmeric dye
Yogurt or fruit cup containers work great!!!
Optional - lemon or vinegar
Write or draw your message: Mix a solution of water and baking soda, start with about 1 Tb soda and ¼ cup water for short messages (may need to make more for a longer secret!).
Dip a cotton swab or paintbrush into the mixture, then draw or write your secret message on the white paper. You will need to reapply mixture to swab several times as you create your drawing or message. Now let it dry completely, can use a hair dryer on low heat setting to help it dry faster. The mixture will disappear, leaving almost no trace of your message or drawing on the paper!
Prepare the developing agent! Into a glass or plastic container, that you don’t mind getting stained yellow, add 1 tsp of turmeric and ½ cup rubbing alcohol. May need to adjust amounts, depending on the quality of turmeric and desired color. More turmeric will give you brighter colors, and less will give more subdued colors. Alcohol should turn yellow and there will be leftover spice on bottom, as it will not dissolve.
If using fresh turmeric root, you will need to grate it first, no need to peel off the outside layer - just grate it all! Then add enough rubbing alcohol to fully cover the grated turmeric (may need more than ½ cup) and let sit for a couple minutes. The curcurmin is extracted almost immediately and will turn alcohol yellow/orange.
Reveal the secret! To read your message, dip a paintbrush into the turmeric developer and paint over the paper. The message will appear red-orange while the rest of the paper is stained yellow! Try to avoid dipping the brush into solid turmeric that settles at bottom. Recommend pouring off the top layer into a new container, discarding the leftover solid.
Optional - hide your secret!! To “erase” the message, simply paint over it with an acid such as lemon juice or vinegar!
Once you erase the message it cannot be brought back. You have to draw or write it again using the baking soda mixture. The acid breaks down the base and it is no longer present on paper, but the turmeric dye will change color again when base is reapplied. How many times can you change the color?
The science behind it: Baking soda is food grade sodium bicarbonate, which acts as a base. The lemon juice contains citric acid and the vinegar contains acetic acid, both of these are acids. The turmeric dye solution contains a compound called curcurmin, that changes color when in contact with base (pH above 8) or acid (pH below 8). Compounds that are considered neutral (pH of 7) do not behave as an acid or base, this understanding of what compounds are and what they can do is called Chemistry!
The paper turns yellow from curcurmin dye because it is not basic (also known as alkaline), but in the areas where the baking soda was applied it will turn bright red-orange, making your secret visible! Then to erase it, you apply an acid to change it back to yellow - resulting in a chemical change! Compounds that are sensitive to changes in pH and change color, are used as pH indicators. Now you can create your own secret codes and share them with friends. Remember, practice makes perfect. Experiment with different amounts of baking soda, turmeric, lemon juice, and vinegar to see how it affects the results. Happy secret-keeping and have fun with this color changing ink!!
Essentially, the turmeric dye acts as a developer, bringing out the hidden message by reacting with the basic baking soda and changing color. Then to undo the color change and erase your message, add an acid such as vinegar or lemon juice.
SAFETY- DO NOT EAT OR DRINK ANY OF THE MIXTURES. Rubbing alcohol or hand sanitizer is flammable, caution and supervision is needed. Also the turmeric dye will stain clothes and hands, but should wash off with soap and water.
Disposal: Dispose of all solid waste in the trash. The liquids can be safely disposed of down the drain with plenty of water.
For toddlers - strongly recommend that turmeric is extracted into water instead of alcohol, color change will be less intense but it is not flammable or stinky.
For older kids - use the alcohol extracted turmeric as an indicator to find out if various solutions in your house are acids (yellow) or bases (red-orange). Some suggestions are window cleaner, salt water, sugar water, milk, juice, carbonated water, etc… start a science journal and take notes to record your observations!!
Figure 1 Source: Zheng, Dantong & Huang, Chongxing & Huang, Haohe & Zhao, Yuan & Khan, Muhammad & Zhao, Hui & Huang, Lijie. (2020). Antibacterial Mechanism of Curcumin: A Review. Chemistry & Biodiversity. 17.
All other images taken by author, Brittany Holmes.
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