In the 1990s, there was a funny robbery case in Pennsylvania, USA. Two men painted their faces with “invisible ink” and then went to rob a bank together. They believed that this magical liquid would prevent surveillance cameras from capturing their faces. However, this trick failed, and they were quickly arrested by the police. This incident later inspired psychologists to study the mindset of these two individuals and speculate on why they would commit such a foolish act.
According to a report by the British Daily Star on September 22, the two main characters in this robbery were McArthur Wheeler and Clifton Earl Johnson. In 1995, they teamed up to rob several banks in the Greater Pittsburgh area. Greater Pittsburgh refers to the metropolitan area surrounding Pittsburgh.
The two men carried semi-automatic handguns during the robberies. They did not disguise themselves, wear masks, or cover their faces with any items. But they were aware that these banks had surveillance cameras and believed that by applying lemon juice, known as “invisible ink,” on their faces, they could make their faces invisible in the camera lens, thus avoiding identification.
However, this trick proved to be useless. Their faces appeared clearly on the surveillance camera footage, leading to their swift capture by the police. Wheeler, upon being arrested, looked at the incriminating footage and exclaimed loudly, “But I applied lemon juice! I applied lemon juice!”
Wheeler claimed that Johnson had told him that lemon juice was the main ingredient in “invisible ink” and that by applying it to the skin, they could disappear in front of the camera lens.
To test this claim, they even conducted an experiment. Wheeler first applied lemon juice to his face and then took a Polaroid camera to take a photo. A few minutes later, when they looked at the picture, Wheeler indeed seemed invisible. As a result, they believed in this theory.
The police explained that Wheeler’s invisibility in the photo was likely due to improper focusing during the shot or flaws in the film.
Wheeler and Johnson were subsequently sentenced to different prison terms. Johnson, for providing evidence against Wheeler, received a 5-year sentence, while Wheeler was imprisoned for over 24 years.
This case was documented in the 1996 World Almanac, sparking the curiosity of Cornell University social psychologist David Dunning, who sought to understand their reasoning logic.
Dunning stated, “If Wheeler was too foolish to rob a bank, perhaps he was also foolish enough not to realize his own foolishness in being unable to rob a bank, meaning his stupidity prevented him from being aware of his own foolishness.”
With the assistance of graduate student Justin Kruger, Dunning conducted a study on this case. The research concluded that individuals with limited knowledge in a certain field often overestimate their expertise significantly because their lack of knowledge prevents them from understanding the full extent of knowledge in that field. This phenomenon is known as the Dunning-Kruger effect.
While lemon juice may not make faces invisible, the liquid can indeed render handwriting invisible and reveal it when needed.
According to IFLScience, all you need is a brush dipped in lemon juice to write your secret message. Let the lemon juice dry on the paper until it appears blank. This way, you have succeeded.
When you wish to unveil these secret messages, simply apply heat from a source such as a hairdryer or a lighter to the paper, and the writing will become visible.
This method is effective because lemon (as well as other citrus fruit) juice contains carbon compounds. When these compounds are heated, they decompose, releasing carbon that reacts with oxygen, causing the color to darken.