Transmitted Infrared photography (IRT) is part of technical photography documentation and enables the detection of underdrawings and pentimenti. It is a highly effective imaging method, as many pigments become more transparent than in standard infrared (IR) photography. The method can be readily implemented using our Technical Photography KIT.

IRT is applicable to artworks on translucent supports, such as canvas paintings, drawings on paper, and historical documents or manuscripts. In the standard setup, the infrared light source is positioned behind the object, while the camera—equipped with an infrared-pass filter—records the transmitted radiation from the front. The light source should be properly shielded so that only radiation passing through the support reaches the camera, and all other light sources in the room should be turned off to minimize stray illumination.

In some cases, it may be useful to test an alternative configuration in which the camera is positioned behind the artwork. However, the front-facing setup is generally preferred, as it produces sharper images: infrared radiation is less diffused after passing through the support before reaching the camera.

Compared to standard IR photography, IRT often provides more informative images for the study of underdrawings, underpainting, pentimenti, and the build-up of pictorial layers. This is particularly evident for white pigments such as lead white and titanium white—widely used before and after the early 20th century, respectively. These pigments strongly reflect incident infrared radiation and therefore remain largely opaque in reflectance imaging, limiting contrast with underlying features. In transmitted infrared, however, radiation passes through the paint layers, allowing hidden drawings and structures to become clearly visible in the resulting IRT image.