The NGV has long applied traditional technical examination techniques to various works of art, including x-radiography, infrared, ultraviolet light and spectral imaging, to observe features not visible to the naked eye. With these diagnostic methods, information is gleaned about surface coatings and underdrawings, structural elements and internal supports, as well as previous alterations and repairs. These methods are often coupled with photography or other imaging technologies, such as Reflectance Transformation Imaging (RTI), to document cultural objects and their physical change accurately and reliably.

Instrumental analytical techniques can also be used to identify chemical and physical properties, such as pigments, resins and binders present in an object. The Conservation department frequently employs two common techniques, X-ray fluorescence (XRF) and infrared (IR) spectroscopy, to investigate the elemental and molecular structures of materials. Ethical considerations are fundamental to conservation which means that scientific research involves careful decision-making particularly with sampling and testing. Non-invasive and non-destructive approaches are always prioritised and preferred by conservators.

X-radiography uses x-rays (x-radiation) to reveal details of an object’s structure and composition. The degree in which X-rays penetrate through different materials is visually represented in an x-radiograph. This example of an x-radiograph was taken of a Persian dish from the 12th century. It immediately shows the numerous pieces that have been adhered together to reassemble the plate. The lighter sections are infills where missing pieces have been recreated.

Under ultraviolet (UV) light many organic materials on the surface of an artwork exhibit varying degrees of UV fluorescence. Varnishes, some paint media and pigments, and various restorations can fluorescence different colours which helps with identifying the material. The image of Hans Heysen’s Sunshine and shadows, 1904-05, is under UV light. The varnish has been partially removed and the remaining varnish on the left half of the painting is visibly fluorescing a characteristic greenish yellow, indicating a natural resin varnish such as mastic and dammar.

Reflectance Transformation Imaging (RTI) is a photographic method where an object is documented multiple times with light falling onto its surface at different angles. When compiled together using RTI computer software, an interactive image is produced that allows close surface examination. This example of a RTI image is of a print by Japanese artist, Totoya Hokkei, depicting a woman making miniature landscape. With RTI, any undulations and creases in the paper become apparent as well as the decorative blind embossing technique known as karazuri in Japan.