Creating invisible ink letters is much easier than you might think; you just need to use common household items.
Simply put, “invisible” letters are those written in such a way that an ordinary person cannot easily read them without employing special methods. For example, the nylon letter written by defendant Thùy Dung in the recent high-profile case involving a beauty and a wealthy businessman is a form of invisible letter.
However, the pinnacle of invisible letters is the “invisible ink” letters – letters that appear to be nothing more than a blank sheet of paper, but contain extensive content the writer wishes to keep secret, except to the recipient.
To write an invisible ink letter, we obviously need invisible ink.
To write an invisible ink letter, we need invisible ink. This ink is made from transparent compounds and can be applied using a bamboo skewer, cotton swab, or even a fingertip. The writing will only become visible under certain external conditions, such as temperature, ultraviolet light, or pH indicators.
It may sound complicated, but anyone can create these invisible letters since the invisible ink can come from items around you. Below are methods for creating such inks.
1. Invisible Ink that Appears with Heat
Any acidic substance can be used to create invisible ink. This includes lemon juice, vinegar, baking soda, white wine, diluted honey, and milk. You can even use diluted urine as invisible ink.
Any acidic substance can be used to create invisible ink.
To make the ink visible, simply hold the paper up to a light bulb or pass it over a flame from a spirit lamp.
Why does this work? The acidity weakens the paper’s structure. Even when the paper dries, the acid remains. Under the influence of heat, that portion of the paper quickly turns brown before the entire sheet catches fire.
2. Invisible Ink that Appears with a Chemical Indicator
This is a more advanced type of invisible ink, as you need to know the necessary indicator for the ink to show, rather than just applying heat. Typically, the indicators are base compounds.
Invisible ink that appears with a chemical indicator is a more advanced type of invisible ink.
Of course, these chemicals are harder to find, but in return, they offer superior security. Here are some examples:
- Phenolphthalein (a pH indicator) and thymolphthalein – visible with ammonia gas or sodium carbonate (or other base compounds).
- Copper sulfate and iron sulfate – visible with iodine salts or sodium carbonate.
- Corn starch or potato starch mixed with baking soda – visible with iodine solution.
Using iodine solution to reveal invisible ink made from starch.
3. Ink Revealed Under Ultraviolet Light
In fact, most inks that are visible under ultraviolet light can also be revealed with heat.
- Diluted laundry soap
- Tonic water
- Vitamin B-12 dissolved in vinegar.
Creating invisible ink is not as difficult as you think.
*Note: You can “disguise” the letter by overwriting it with another content using a ballpoint pen, pencil, or crayon. Do not use ink pens, as the ink may bleed into your “invisible” layer.
