After studying the paint surface, we can remove tiny paint samples, no larger than the head of a pin. These samples cut across the layers of the painting: the varnish, the paint and the ground. Because taking a sample involves permanently removing part of the paint layer, the technique is used sparingly. This type of cross-section can help us to investigate the composition and structure of the paint layers. The paint sample is prepared for examination by pouring it into a small block of synthetic resin. After the resin cures (that is, hardens), it is ground down and polished until only an ultra-thin layer of resin remains. Through the resin, the paint layers are visible on the surface. An optical microscope is used to magnify the paint sample 100 to 1,000 times. The researcher examines the sample under normal and ultraviolet light. This makes it possible to study not only the composition of the paint layers, but also the individual particles of pigment.