This type of invisible ink can be seen through glasses and can be used to create secret messages on paper. This type of invisible ink can only be seen by using a pair of special sunglasses or a light emitting a specific wavelength. This ink can be used by spies as a way to transmit secret messages, which cannot be seen by the naked-eye.
There are several types of invisible inks, including heat activated ink, light activated ink and chemically activated ink. Heat-activated ink can be made using substances that glow when heated, like laundry detergents and human saliva. Chemical-activated ink is made by using an invisible solution that changes color when exposed to certain chemicals, such as methyl ethyl ketone or nitrocellulose. Light-activated Ink is made using invisible ink which only becomes visible when exposed to a specific wavelength of light such as ultraviolet or IR.
The longevity of invisible ink varies depending on the type and quality of the ink, as well as the conditions under which it is stored. Inks of higher quality can last for many years when stored properly. Low-quality invisibles inks, on the other hand, may only last several days. Some invisible inks only appear when exposed to certain wavelengths of light such as infrared or UV, while others can only be viewed when viewed with a filter that blocks the wavelength of light.