One of the methods used to examine artworks is optical microscopy. Taking all appropriate precautions, tiny samples (the head of a pin or smaller) of the work are taken and placed under a special microscope, called an optical microscope. By examining these samples under the microscope conservators are able to learn a lot of information about the work and how it was made. The procedure identifies what processes the painter or iconographer applied to the work, e.g. what kind of preparation was applied to the wood or on the fabric to make it smooth and primed to receive paint. The microscopic process also reveals the type of pigments, mediums, and the order of paint application, along with the era the mediums came from, whether it consists of modern paint pigments or older ones that are made of powder granules. The analysis also shows how many layers the painting has and how many layers of varnish have been applied. All of this is important information in the analysis of artworks. This also gives the ability to ascertain what type of paper was used by the artist in a drawing, what type of wood was used by an iconographer on a wood panel, and what type of cloth was used to create a painting. There are incidents when new images have been drawn over an existing painting, covering the original work of the artist. For example, there was a time in history when paintings displaying nudity were painted over to include clothing. With optical microscopy these cases can be identified and any additional painting applied after the time of the original painted image can be discovered.