How does invisible ink work?

Ultraviolet (UV) light makes certain stamp inks visible through fluorescence, a process where inks containing fluorescent dyes absorb UV light and re-emit it as visible light. When exposed to UV light, these dyes' electrons are excited to a higher energy state and release energy as they return to their normal state, emitting visible light in various colors. This creates a contrast between the ink and its background, enhancing visibility. This property is particularly useful in security printing, where such inks help prevent counterfeiting by remaining visible only under UV light.

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