Examination under visible light is the first and foremost technique for investigating the surface of objects. Typically, conservators will spend from minutes to hours examining an object before they begin treatment. Visible light is the first and foremost method for examining an object and, often, such examination is all that is required.
Different aspects of an object can be revealed depending on the spectrum and angle of incidence of visible light. Below you can see images where oblique lighting is used to document the differences in the surface of a Chinese rubbing before and after treatment; the gnomon at the left-hand side of the pictures shows the direction of the illumination. You can see another example of the use of oblique lighting in our Thangka project page.
Chinese rubbing, before treatment:
the folds and tears in the paper of the rubbing are revealed by oblique light.
Chinese rubbing, after treatment:
the tears are repaired and the folds are reduced. The gnomon at left of the image shows that the lighting angle is comparable in the two pictures.