There are many types of images used for a variety of different purposes in the field of Conservation today, such as standard visible photography, X-radiographs, and UV and IR examinations. Here one of the simpler forms of imaging, 'Raking Light' photography, will be discussed.
Raking Light involves shining a strong light directly across the surface of a painting, highlighting any surface irregularities. Features such as brush strokes, damages, raised paint and planar deformations all become more defined due to the shadows they create across the surface of the painting.
This form of examination is commonly used to document the condition of the surface of a painting before, during and after conservation.
Details from: Christ Mocked, Hieronymous Bosch, : ~1490 Oil on Oak, 73.8 x 59 cm. NG4744. The colour image on the left represents the standard visible examination and the black and white image on the right shows a Raking Light image taken of the same area.
The normal approach to a Raking light examination is to set your painting up on an easel and then adjusted the light to clearly define as much of the surface detail as possible. The exact position and angle of the light is often difficult to record, making it nearly impossible to reproduce the same conditions for further raking light examinations of the same painting later on during the conservation process.
Also if a Raking Light photograph is taken it only records the image with light coming from one particular direction. The direction of the light, as stated, is normally chosen because it produces what appears to be the most information. However, even though the chosen light angle hight lights much information it does not necessarily highlight all of what could be important.