Unveiling the Secrets – Marking Cards with Invisible ink
In the olden days, spies wrote secret messages with invisible ink. It may seem old-fashioned, low-tech in comparison to the high-tech communications we have today, but invisible writing can be used for a variety purposes.
The first step to making invisible ink involves mixing the ink solution. This is made by mixing water with a liquid which is slightly acidic such as lemon or vinegar. This mixture can either be applied with a brush or a pen. To reveal the message, the paper must be heated. This can be done by ironing the paper, placing it in an oven (with care to prevent burning), or holding the paper over a light bulb.
Depending on the type of ink used, different acids are needed to make it visible. Citric acid in lemon, for example, is what causes the paper to carbonize and brown. You can reveal other invisible inks by spraying, wiping or shining ultraviolet light onto the paper.
Use invisible ink for writing messages is an engaging and fun way for students improve their writing. This method can be used to highlight a specific skill that you’d like your students to focus on, such a capital letters or writing complete sentences.