We often examine a painting with transmitted visible light and infrared radiation. In particular, 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.
So, we are releasing a new Pigments Checker with a translucent support, such that of a canvas painting. Now you can use Pigments Checker to practice also those useful and effective imaging methods implying transmitted radiation. With Pigments Checker v.5 you can now practice Transmitted Infrared photography (IRT) which 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 This method is useful for art on translucent supports, such as paintings on canvas, drawings on paper and historical documents and manuscripts.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 focus 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 (actually diffused infrared).
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 of the figures. IRT is so powerful in particular for white pigments, such as lead white and titanium white, the most common in the art, very important white pigments in art, are 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.