Infrared Reflectography (IRR)

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Imaging > Imaging Techniques > Infrared techniques > Reflected Infrared Imaging

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Infrared reflectography (IRR)[edit | edit source]

Definition[edit | edit source]

Infrared reflectography is a technique that uses wavelengths in the infrared range of the electromagnetic spectrum to penetrate through opaque paint layers and reveal otherwise invisible elements of the composition. Infrared light is absorbed by carbon-rich materials and reflected back from light-colored elements such as a white ground. Compared to reflected infrared photography, detector systems record a wider range of wavelengths – in different infrared spectral bands from 900 nm to 2500 nm – allowing for even greater penetration of different colors. As most cameras are relatively low resolution, infrared captures are acquired in small segments while scanning the surface of an artwork. These are digitally assembled to produce a full picture called an infrared reflectogram mosaic.

Silicon based CCD and CMOS sensors common in most commercial cameras will not be able to detect wavelengths beyond ~1000 nm. As such, a specialized camera with a different type of detector or sensor (eg: vidicon tubes, InGaAs) will be required.

Common uses[edit | edit source]

Introduced in the late 1960's, it was initially successful primarily in revealing underdrawing in Early Netherlandish painting. Increasingly sophisticated sensors using the full range of the infrared spectrum with higher sensitivity and better resolution are now able to reveal other features of a painting, such as pentimenti and underpainted sketches, even on paintings with a darker ground.

Equipment[edit | edit source]

Cameras[edit | edit source]

InGaAs sensor[edit | edit source]
Apollo/Osiris[edit | edit source]
Goodrich/Sensors SWIR[edit | edit source]
PtSi sensor[edit | edit source]

Lenses[edit | edit source]

APO macro lens: JENOPTIK UV-VIS-IR 60 mm 1:4[edit | edit source]
Edmund Optics SWIR lenses[edit | edit source]

Detectors[edit | edit source]

Types of detectors[edit | edit source]
Photon detectors[edit | edit source]
Thermal detectors[edit | edit source]
Detectors materials[edit | edit source]
InGaAs detectors SWIR (1-3 μm)[edit | edit source]
InSb for 5 μm MWIR imaging[edit | edit source]
DTGS detectors (MWIR)[edit | edit source]
Hg1-xCdxTe alloys for 5 and 10 μm LWIR imaging[edit | edit source]
Quantum well detectors for 5 and 10 μm imaging[edit | edit source]
Uncooled bolometers for 10 μm imaging[edit | edit source]
Pb salts detectors (Pbs and PbSe)[edit | edit source]

Light sources[edit | edit source]

Tungsten incandescent[edit | edit source]
Tungsten halogen[edit | edit source]
IR emitting LED[edit | edit source]
Xenon strobe[edit | edit source]
Silicon carbide (Globar), Molybdenum silicide or ceramic element heated at 1100-1400 K[edit | edit source]
Synchrotron free electron laser[edit | edit source]

Calibration[edit | edit source]

Capture/ Workflow[edit | edit source]

Image processing[edit | edit source]

Registration[edit | edit source]

Troubleshooting[edit | edit source]