Thanks to the technique of infra-red reflectography, we can see the preparatory drawing which formed the structure and composition of these paintings beneath the paint layers. In some cases relating to fifteenth- and sixteenth-century painting, the reflectographs are the only means of seeing drawings by artists whose works on paper have not survived. It has thus been possible to discover the graphic style of artists such as Robert Campin, Memling and Pedro Berruguete, whose drawings would otherwise be completely or almost totally unknown to us. Drawing is of course a highly personal and unique mode of artistic expression for the painter and can thus be seen as a document as well as a piece of artistic evidence of primary importance for the study of the work of certain artists and the attribution of their works.
The technique of infra-red reflectography has been in use for various decades since the late 1960s. However, new digital technology has allowed for a greater penetration of the paint layers and consequently a better quality of image. From 2002, the Museo del Prado's Technical Documentation Department has undertaken a research project which has revealed under-drawings of fifteenth- and sixteenth-century panels with a truly astonishing clarity and precision. The project is the result of a joint collaboration with the Optical Metrology Laboratory for the Study of Works of Cultural Heritage (part of the Istituto di Fisica Generale Applicata in Milan) and has also involved the Galleria degli Uffizi and the Accademia Carrara in Bergamo.
The results of this project will be displayed in the exhibition, which combines both scientific interest and the revelation of the hidden beauty of these works. Featuring the display of infra-red images and of the paintings themselves, The Hidden Line is divided into two sections. The first part shows the variety of drawing techniques evident in the under-layers of the paintings in question (brush, stencil, squaring-up, black chalk, charcoal, silver-point, etc) as well as the changes made to these works during the course of their design and execution. The exhibition then displays the images arising from the research project, allowing for a direct comparison of the finished paintings with the beauty and subtlety of the under-drawings in these important examples of fifteenth- and sixteenth-century Flemish, Italian and Spanish paintings.