A compositional change by the artist, often referred to as pentimenti (from the Italian pentimento meaning repentance) can often be detected on close inspection with the naked eye or with the aid of a strong raking light across the surface from one direction.
Inconsistencies in the surface texture or an unexpected texture in the paint layers can point to the existence of an underlying design. Wear, loss or transparency in the upper paint layers may also lead to changes being revealed.
In addition, cracks in the upper layers of paint may show surprising colours below. Further information will be gained using increasing degrees of magnification.
X-rays are one of the methods of analysis used by conservators in the examination of works of art that allow us to see further than is normally possible.