Would shooting in infrared increase visibility of handprints on a wall? I currently need to shoot some photos of some faint handprints a child made on a wall many years ago. Thanks
IR photography might work, but I have a feeling that you might do better with UV photography. There's a good bit of research and writing on forensic photography which may apply here. Like this report. (Report details result using different wavelengths of light as captured using differing light sources and photo filters)
I don't have any affiliation with these guys (Life Pixel) but they do IR and UV conversions. Might be worth seeing if you can rent a camera from them to do some testing in your scene to see what works best.
From my practical experience with infrared imaging, many materials tend to be less absorptive (meaning less contrast) in the near infrared. As has been already said, UV might be a good bet because many body fluids show fluorescence under UV light.
Theoretically, spectrophotometric imaging could also be an option to incease contrast for selected substances, but this is way too elaborated for an average photographer.
Rent or borrow a Long Wavelength UV light source to illuminate the scene.
The scene can then be photographed with any normal camera. The source will fluoresce the stains to make them more visible against the ambient background.
You do not need a UV converted camera sensor as the subject of interest is converted to visible wavelengths under the UV source.
Note: Other things not immediately evident may also be revealed by the source. Rather repulsive body fluids can also be visible as well as different building materials and treatments (polyfilla, paints, and woodstains).
I think the difficulty is that different materials will react differently to IR and UV light. Trying a variety of lighting is probably going to be your best bet.
Keep in mind that you have no idea what the handprints are made of, so you really can't even research how to take pictures of fingerprints or fresh hand prints because after years and years even if it started out as skin oil, that's been replaced by dust or even corrosion of the surface.