IR Reflectance
Definition
Imaging under near-infrared illumination (715-1000 nm) to differentiate inks by their IR absorption: carbon-based inks remain dark, many synthetic dye inks become transparent, revealing text beneath obliterations.
- Wavelength range
- Near-infrared light typically used is 715-1000 nm
- Ink types affected
- Carbon-based inks remain dark, synthetic dyes often become transparent under IR
Common questions
How does IR reflectance help read overwritten or covered text?+
Different inks absorb and reflect infrared light differently. When one ink covers another, an IR camera can see through the top layer if it becomes transparent under infrared illumination, revealing the hidden text beneath. Carbon-based inks stay dark while many synthetic dyes become see-through.
Why do some inks disappear under infrared light?+
Many synthetic dye inks are transparent to near-infrared wavelengths (around 715-1000 nm), while carbon-based inks absorb the light and remain dark. This selective absorption is what makes IR imaging so useful for document examination and ink differentiation.
What can investigators find using IR reflectance imaging?+
IR reflectance is used to read text that has been struck through, overwritten, or obliterated by crossing out with same-colored ink. It can also differentiate between inks that look identical to the human eye by capturing their different infrared signatures.
Related terms
- Acid-Free Packaging
- Paper folders or envelopes manufactured without acidic buffers, used for long-term storage of questioned documents to prevent acid-catalysed paper and ink degradation.
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- Detective Dye
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- Electromagnetic Spectrum
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- ESDA (Electrostatic Detection Apparatus)
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- Fluorescence
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- IR Luminescence
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- Neutron Radiography
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- Oblique Illumination
- Lighting applied at a very low angle to the document surface (below 10 degrees from horizontal) to reveal topographic features: writing indentations,...
- Transmitted Illumination
- Lighting passed through the document from the back face to reveal paper-body features invisible from the surface: watermarks, security threads, and paper-thickness...
Explained in these topics
- Crime Detection Devices: UV, IR, X-Ray and Detective DyesSelective absorption or reflection of IR by inks, dyes and biological materials. The mechanism that lets IR cameras read writing covered by overwriting ink of...
- Lab Equipment, Evidence Handling and Chain of Custody in QDEImaging under near-infrared illumination (715-1000 nm) to differentiate inks by their IR absorption: carbon-based inks remain dark, many synthetic dye inks bec...