A technique used in tracing a drawing from one side of a leaf to the other by placing a strong light source on the other side of the leaf being illuminated and a weaker light source behind the artist (used in the Lindisfarne Gospels in the early eighth century and described as a technique by a fifteenth-century artist Cennino Cennini in his handbook 'Il libro del'Arte'). See also backdrawing.
Michelle Brown. Understanding Illuminated Manuscripts. (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).