underdrawing

underdrawing.
Preliminary drawing made on the prepared canvas, panel, or other support before the application of paint. Underdrawings are obviously not meant to be seen after the picture is completed, but they are sometimes visible to the naked eye in thinly painted passages, as well as in unfinished works. They can also be revealed through infra-red photography or through the related technique of infra-red reflectography (which can achieve greater penetration of the paint layers), developed in the 1960s by the Dutch physicist J. R. J. van Asperen de Boer. Many paintings have been examined by these methods, particularly 15th- and 16th-century works, revealing underdrawings that range from summary sketches to highly finished compositions. They can be useful tools in matters of attribution.