Transmitted Infrared photography (IRT) is part of the Technical Photography documentation and allows to detect underdrawing and pentimenti. It is a very effective imaging method since pigments become even more transparent than in the usual IR photography method. This method can be realized with our Technical Photography kit.

This method is useful only for art on translucent supports, such as paintings on canvas, drawings on paper, and historical documents and manuscripts. The lamp providing IR radiation should face the back of the painting while the camera focuses on the front.  The lamp should be shielded so that only the radiation through the canvas can reach the camera. Any other source of radiation in the examination room should be turned off to avoid diffused light.
In some cases, it could be worth testing the method changing the front-facing configuration and having the camera facing the back of the painting. In general, the first setup is preferred because
the drawing lines will appear sharper since the infrared will not be diffused by the canvas.

IRT often provides better images compared to IR for detecting underdrawing, underpainting, pentimenti, or just the actual build-up technique of the painter to shape the figures. IRT is so powerful in particular for white pigments, such as lead white and titanium white, the most common in art, the most used, respectively, before and after about 1920′. These pigments reflect a lot of the incoming infrared and, consequently, their hiding power is barely affected by infrared coming from the front. They will just reflect most of the IR and they will not produce contrast between the ground and the underdrawing. When the infrared radiation comes from the back (transmission), the infrared can penetrate the paint and the underdrawing becomes apparent in the resulted IRT image.