Which nondestructive lighting technique can reveal chemical alterations in documents?

The use of shortwave and longwave UV light is particularly effective for revealing chemical alterations in documents due to the way different substances interact with ultraviolet radiation. Many inks and other materials used in documents fluoresce or absorb this UV light differently compared to the substrate (such as paper). This variability allows investigators to see modifications that are otherwise invisible under standard lighting conditions.

For example, specific chemicals or inks may glow prominently under UV light, highlighting areas where alterations have been made, such as erasures or the addition of new text. This technique is commonly utilized in forensic investigations, as it is both nondestructive and highly effective in detecting subtle changes in documents without damaging the original materials.

In contrast, methods like X-ray imaging and fluorescent gel analysis are used for different purposes in forensic science. X-ray imaging can reveal structural details but may not specifically highlight chemical alterations. Fluorescent gel analysis is often used for biological samples rather than document examination. Standard white light does not provide the same contrast for chemical variations, as it lacks the specific wavelengths needed to stimulate fluorescence in certain materials. Thus, for the specific task of revealing chemical alterations in documents, shortwave and longwave UV light stands out as the appropriate technique.