Paint Surface Micrography
Paint surface micrography is a non-destructive means of analysing the basic pigment structures contained within a painting. This approach allows for a rapid initial assessment of the paint structure, providing enough visual information to establish a basic understanding of the approximate period of the work in question. This methodology is used as an initial guide when analysing pigments for dating purposes, but conclusions must be corroborated with more accurate spectral or chemical analysis. The below image depicts the flesh tone on a 17th century portrait painting. The pigment granularity here exhibits a coarseness to be expected of hand ground mineral pigments. The large crimson/burgundy coloured crystals are made of Cinnabar, also known as Vermillion, a red lake mineral pigment in common use until the advent of Cadmium Red in the 19th century. The visible flecks of black are formed of “Ivory Black” – charred and ground bone.
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Image: Magnified detail of a flesh tone from a 17th century oil painting on canvas support.
IR Spectroscopy is one of several forms of spectroscopic analysis. This non-destructive methodology captures the unique spectral properties (often called “spectral fingerprint”) of different materials – in this case artists pigments – when contacted by a beam of infrared light. Certain pigments respond better to infrared based spectroscopy (i.e. FTIR – Fourier Transform, and NIR – Near Infrared), while others are more responsive to Raman Spectroscopy, and XRF (X-Radiography Fluorescence). ArtGenomics offers NIR spectroscopy as a non-destructive, non-invasive, means of pigment analysis.
Image: A spectral cross comparison of scans from two samples of natural cinnabar.
Dendrochronology (“dendro” for short) is a form of tree ring analysis that can be used to establish an approximate dating for a piece of wood, and is also useful in the dating of works of art on wood panel support. Since the 1970s dendro has been used to successfully date countless panel paintings and is now widely accepted as a valuable investigative tool in the field of technical art history. Provided that a good reading can be taken from a given sample, dendro analysis should be able to provide at least the earliest possible date that a tree could have been felled. This is known as the “terminus post quem”. Data collected for the purposes of dendrochronology can also be used to establish the approximate location of the tree before it was felled. This is a branch of dendrological analysis known as “dendroprovenancing”. There are specific limitations to the application of dendro analytical techniques, particularly in relation to sample quality and databasing, though overall dendro offers a useful additional toolset in working to establish a timeframe and location for the origin of a panel supported painting. ArtGenomics offers detailed dendrochronological reports for works of art on wood panel dating earlier than the 20th century.
Image: Graphical comparison of sample ring width variances.