Reflected infrared imaging revisiting the fundamentals

Reflected infrared imaging has been used as an investigation tool for paintings and paper conservation since the 1930s. The technique can reveal underdrawings, expose compositional changes, provide information about manufacturing process and technique, and differentiate materials. As digital camera technology and computing have evolved, the technique has continued to advance, improving the applications for cultural heritage documentation. However, there is very little published on the use of the technique for three-dimensional cultural heritage object documentation. The term object refers to three-dimensional works of art that include archaeological, ethnographic, historic, sculptural, decorative, and contemporary arts, composed of a wide variety of materials and combinations of materials. Some of these materials are similar to those in paintings and others are quite different, and the optical properties of the materials influence the interaction with infrared radiation and the imaging results. This paper looks at the current applications of reflected infrared imaging in conservation and research documentation and explores the fundamentals of why the technique is successful and how that success might transfer to the documentation of 3-D objects. Examples from an imaging case study with the Freud Museum are included to illustrate the arguments.