Infrared Photography (IR)
Infrared photography (IR) is a fundamental technique in technical photography, widely used for the examination of artworks and cultural heritage objects. Its primary application is the detection of underdrawings—preparatory sketches beneath the visible paint layers—by exploiting the ability of infrared radiation to penetrate certain pigments. Beyond revealing underdrawings, IR imaging can also provide valuable information on materials, compositional changes, and areas of restoration across a wide range of artifacts, making it an essential, non-invasive tool for art examination and conservation.
Table of Contents
Photographic set up
The infrared (IR) photographic setup shown in the image uses a controlled illumination and filtering system to isolate reflected infrared radiation from the artwork. The ELIO halogen lamp acts as a broadband light source, emitting both visible (VIS) and infrared (IR) radiation toward the surface. The artwork reflects these components differently depending on the materials and underlying layers. The IR-pass filter of the ROBERTINA filters set is placed in front of the camera lens to block visible light and allow only infrared wavelengths to reach the sensor. As a result, the camera records an image based solely on infrared reflectance, which can penetrate certain paint layers and reveal underdrawings or compositional changes. The diagram also highlights how different layers—such as varnish, paint, and ground—interact with IR radiation, enabling deeper visualization compared to standard visible-light photography.
For more info download: “Infrared Technical Photography for Art Examination”
Hot Spot
In infrared photography, hot spots are unwanted bright areas—usually circular and centered in the frame—that become visible when using infrared light. They are caused by internal reflections within the lens, where infrared wavelengths bounce between lens components (especially coatings and aperture blades) and concentrate light toward the center of the image. Unlike visible-light photography, lens coatings are often not optimized for infrared, making some lenses more prone to this effect. Hot spots are typically more noticeable at smaller apertures (higher f-numbers) and in scenes with even illumination, such as skies or flat surfaces. Because they can degrade contrast and image quality, infrared photographers often test lenses in advance and prefer models known to be “IR-friendly,” minimizing or eliminating this artifact.
The Nikon 50 mm lens included in the Technical Photography KIT exhibits a very low hot spot effect, making it our recommended all-purpose lens for infrared photography, suitable for everything from close-up work to architectural subjects. Check it out in our Infrared Hot Spot Lens Database.
ELIO, the halogen lamp
The Elio halogen lamp is a reliable and versatile light source designed for technical photography, delivering a continuous, stable spectrum that closely resembles natural illumination. Its strong output and consistent color temperature make it ideal for accurate documentation, material analysis, and controlled imaging conditions, including infrared photography where predictable performance is essential. Built for precision work, the Elio lamp ensures even illumination and repeatability across sessions, allowing photographers and researchers to capture consistent, high-quality results in both laboratory and field environments.
Furthermore, halogen lamps are an excellent source of infrared radiation for documenting large artworks, such as wall paintings.
Infrared Imaging of Heat-Sensitive Materials
For the infrared documentation of heat-sensitive materials, such as manuscripts, LEDs and electronic flashes are particularly suitable light sources. Unlike halogen lamps, they emit minimal heat while still providing sufficient infrared radiation for imaging, reducing the risk of thermal damage to delicate objects. Their controlled and often directional output also allows for precise illumination, making them ideal for careful, conservation-focused photography.
Pigments Checker
Pigments checker is a calibrated reference chart used primarily to verify the performance of photographic equipment in infrared imaging. It contains a selection of pigments with well-known infrared responses—some that become transparent and others that remain opaque. By photographing the checker under the same conditions as the artwork, users can confirm that their camera, filters, and light source are correctly capturing the expected degree of pigment transparency. If the recorded image shows the same pigments becoming transparent (or not) as in standard references, it indicates that the setup is functioning properly. In this way, the pigment checker serves as a practical control tool, ensuring consistency, reliability, and comparability in technical photography.
IR versus IRR (Infrared Reflectography)
Infrared photography (IR) and Infrared Reflectography (IRR) differ primarily in the wavelength range they can record and, consequently, in their analytical potential. A standard full-spectrum digital camera is typically sensitive up to about 1100 nm, while IRR—performed with an InGaAs camera—extends this range to approximately 1700 nm. The longer wavelengths accessible with IRR can, in some cases, penetrate deeper into painted layers, as certain historical pigments become more transparent in this region. However, this effect is not universal: only some pigments show a significant increase in transparency, and in many instances the difference is minimal. Therefore, while IRR can offer advantages for specific materials and applications, its benefits depend on the particular pigment composition and should not be assumed in all cases. More detailed information is available on the Infrared Reflectography page.
Resources
| Publications on Infrared Photography (IR) |
|---|
| A. Cosentino “Infrared Technical Photography for Art Examination” e-Preservation Science, 13, 1-6, 2016. |
| A. Cosentino “Identification of pigments by multispectral imaging a flowchart method” Heritage Science, 2:8, 2014. |
| A. Cosentino “Effects of Different Binders on Technical Photography and Infrared Reflectography of 54 Historical Pigments” International Journal of Conservation Science, 6 (3), 287-298, 2015. |
Case Studies using IR Photography
Case study #002. 16th-century Antiphonary parchment sheet
20th-century serigraph print
Early 20th-century Persian manuscript with a drawing attached over the text
17th century Umbrian School Madonna and Child
15th-Century Icon – Modern Study Replica
19th-century icon Saint Nicholas
19th-century Sikh school miniature painting
Mid-20th century Italian test plate for underglaze colors
19th-century Color Chart “Ratti Ernesto & C” – Turin -Italy
Learn Technical Photography for Art Examination
Technical Photography is one of the most powerful—and often overlooked—tools for the scientific examination of art and archaeology. If you are a conservator, scientist, or art collector and you are not yet familiar with this method, it is truly a missed opportunity. Using simple, affordable equipment and a clear methodology, Technical Photography allows you to reveal underdrawings, retouchings, material differences, and conservation issues in a completely non-invasive way. Far from being complex or inaccessible, it is an easy entry point into scientific analysis. In many cases, Technical Photography represents the first essential step toward a deeper understanding of artworks and archaeological objects.
Scientific Art Examination – Resources:
Getty Conservation Institute (GCI) – USA
The British Museum – Scientific Research Department – UK
Scientific Research Department – The Metropolitan Museum of Art, New York, USA
C2RMF (Centre de Recherche et de Restauration des Musées de France) – France
Rijksmuseum – Science Department – Netherlands
