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Infra-red reflectography & watermarks

Infra-red reflectography and its use in the examination of works of art

home | Infrared | Microscopy 1 | 2 | X-rays


  S.T. Gill, Noon. Watercolour on paper 19th Century Collection of the National Gallery of Australia
ST Gill 'Noon' 19th century Watercolour on paper Collection National Gallery of Australia

Detail of Noon by S.T. Gill. Infra-red reflectogram, showing underdrawing

Detail of 'Noon' Infra-red reflectogram, showing underdrawing


Infra-red light lies just outside the visible spectrum, overlapping with the visible spectrum on one side and with the microwave region on the other. Conservators work with infra-red light in the region of 750-1800 nanometers. (One nanometer is one billionth of a meter). Wavelengths of infra-red light are relatively long and low frequency, allowing them to penetrate through the upper layers of a work. This means that varnishes and some pigment layers become transparent, revealing underdrawing and other hidden details. However, not all pigments become transparent, some remain opaque. So infra-red examination can be used as a tool to differentiate between certain groups of pigments, inks and areas of change, such as later retouching. This information is usually captured on special photographic film or digitally using an infra-red vidicon, translating the invisible image into one our eyes can see.

Infra-red examination is routinely applied in the analysis of an artist's working technique. The infra-red vidicon has been used here to record a detail of a 19th century watercolour, Noon, by S.T. Gill. The thin washes of watercolour are easily penetrated revealing the artist's confident handling of the underdrawing. Features of the landscape, animals and figures have all been loosely outlined with a graphite pencil. Although some of the underdrawing is visible to the naked eye, the pencil lines are enhanced in infra-red, making clearer those areas of the design obscured by thicker paint.


shim Henri Matisse, Blouse Romaine, 1938. Charcoal on paper. Collection National Gallery of Australia.
Henri Matisse 'Blouse Romaine' 1938 Charcoal on paper Collection National Gallery of Australia
shim beta-radiograph from lower left corner, showing chain and laid lines and watermark of a nude with a ribbon.
βeta-radiograph from lower left corner, showing chain and laid lines and watermark of a nude with a ribbon


When examining works of art on paper, conservators look at the structure of the paper support. The presence of features such as watermarks and chain and laid lines can assist in the identification of the place and time within which the paper was made. This may be critical to determining the authenticity of a work, and provides interesting historical information.

Watermark symbols are unique to the paper mill where the paper was produced. However as they can be used for many decades, determining the age of the paper can involve technical analysis of fibres, size, and fillers. Occasionally a watermark will include a date; but more often less obvious details such as the stitching marks surrounding a watermark will provide a clue to the age of the paper. Conservators record these structural details using transmitted light photography, or if the image layer is dense, using a form of X-ray called βeta-radiography.

Matisse's charcoal drawing Blouse Romaine 1938 was documented using βeta-radiography, and the image analysed by paper historian Peter Bower. The watermark of a nude with a ribbon signifies that the paper was made by Gaspard Maillol at Montval in France, which he operated between c.1910 and the 1940s. This watermark was designed by the French artist Aristide Maillol, uncle of Gaspard. Aristide was involved in establishing the mill and also collaborated with Gaspard on the production of papers suited to his publishing and artistic requirements. By the 1930s the mill was producing a range of papers primarily for printmaking, and special edition book production. These were taken up as drawing papers by artists who included Picasso, as well as Maillol's friend Matisse. The paper used for Blouse Romaine is a typical warm toned hemp and linen paper, produced at Montval in the 1930s.

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