Forensics

Historically, paintings could be verified with reasonable assurance of authorship by experts who knew the brushstrokes and color and paint choices of the artist as well as the overall style and character of the subjects. However, in some cases, fraudulent artworks have been successfully passed as genuine. New techniques for assessing all types of artwork are always needed, and the scientific community has been answering the call. One scientific technique for checking the authenticity of old paintings uses laser lights. How might this feat be accomplished?

Answer

Until the mass production of paints became available in the late 1800s and early 1900s, each paint used by an artist is known to contain atoms in particular characteristic amounts, depending on the source. Paints were originally made from natural materials, so when an artist mixed his or her paints, there was usually a unique mixture of atoms and molecules for each color and color combination.

Different atoms absorb and emit their unique characteristic frequencies of light in the visible and the ultraviolet. The types of atoms present and the intensity of the characteristic spectrum from each atom type will create a “spectral fingerprint” for each artist. As you know, some artists simply laid out the design of the painting, for example, and lesser painters filled in the regions, with the master artist completing the final touches. Even these paintings have their own fingerprint of spectral colors.

With a tunable laser capable of scanning from the infrared frequencies to the ultraviolet frequencies, the “spectral fingerprint” of any region of the painting can be recorded and compared to other paintings by the same artist or even other artists, including fraudulent painters. This laser approach is normally combined with other approaches to achieve the comprehensive evaluation.

The laser technique also permits the identification and removal of environmental coatings on top of the paint beneath, such as dust and grime, and ensures that no harm to the painting occurs. Famous paintings such as Rembrandt’s 1642 De Nachtwacht (The Night watch) in Amsterdam’s Rijksmuseum have had the soot and grime safely cleaned off to reveal a marvelously brighter background of faces when compared to the somewhat obscure dull background that had existed for centuries.