Why can ancient paintings be identified by ultraviolet rays?

Ultraviolet light is invisible light, which lies outside purple light in the spectrum. The frequency range is 5×106 ~ 7.5×1014hz.

Natural ultraviolet rays on the earth come from sunlight.

The main feature of ultraviolet light is its strong chemical action. It is easy to make photographic film sensitive. In addition, ultraviolet rays have a strong physiological function and can kill bacteria. Ultraviolet rays can make fluorescent substances glow, and anti-counterfeiting can be carried out by applying the fluorescence effect of ultraviolet rays. For example, the ultraviolet rays emitted by the money detector can make the fluorescent substances on the banknotes glow (and can also make the fluorescent substances on the anti-counterfeiting trademarks glow). In addition to using this effect on the money detector, we can also use the characteristics of different substances emitting different colors of fluorescence under ultraviolet radiation to identify ancient paintings.