TRACING THE TESTS
by Andrew Vowles
In 1993, Lloyd Sullivan took his family heirloom to the Canadian Conservation Institute (CCI) in Ottawa. Run by the Department of Canadian Heritage, the institute conducts restoration and scientific work for public institutions such as museums and art galleries.
The Sanders portrait was subjected to numerous tests arranged through CCI’s Analytical Research Laboratory. In a newsletter published in late 2001, CCI scientists wrote about their examination of the painting. That examination had been prompted by a question: Could a scientific study of the portrait and its materials determine whether or not the painting dated from the early 17th century?
An early — and key — step was to date the wooden panels the portrait had been painted on to corroborate the date of 1603 painted on one corner of the portrait itself. Peter Klein, a dendrochronologist from the University of Hamburg, found that the wood was oak from the Baltic region.
His examination of the tree rings showed an earliest possible date of 1597 for the painting.
Next, the institute used radiography to find out whether the portrait had been painted over an older picture. (Like a medical X-ray used to show bones beneath the skin, these X-rays would pass through and show any earlier painting.) After that test turned up no under-painting, the scientists used two kinds of special photography to look for signs of major retouching.
Guelph physics professor Diane Nalini De Kerckhove explains that shining ultraviolet light on the painting would cause fluorescence wherever it had been retouched. But the test showed up no such evidence, a result corroborated by infrared photography.
Now the scientists turned to the paint itself. Learning what elements were in the paint might help expose a fake. Finding, say, cadmium pigments that became available to artists only in the 19th century would have raised serious questions about the painting’s authenticity. Using REXES (radioisotope-excited X-ray energy spectrometry), the researchers compared the resultant X-ray pattern from minuscule paint samples with a huge database of known chemical elements.
From lead white to cinnabar, all the elements in the portrait had been in use by early 17th-century artists. The scientists also studied a minute cross-section of the painting sliced from the varnish all the way through the paint layers to the oak board. They found that the materials and how they were made matched the style — so-called Northern School — of the time in England.
Flipping over the portrait, the CCI scientists focused on a label affixed to the back of the panel. Today most of the label has flaked and rubbed away, leaving only traces of black ink from writing that is no longer legible to the naked eye. But an earlier transcription reads as follows: Shakespere. Born April 23, 1564. Died April 23, 1616. Aged 52. This likeness taken 1603. Age at that time 39 years. (That transcription was done in 1909 by a man named Spielmann, who had examined the portrait and concluded that it was a relatively modern copy or fake.)
CCI analysis showed that the label had been made from linen rags, a common source of paper in Shakespeare’s time. Scientists managed to scrape off a few milligrams of the paper, enough to share with a physicist at the IsoTrace Radiocarbon Laboratory at the University of Toronto. Using standard radiocarbon-dating techniques with a sophisticated accelerator mass spectrometer that allows a “look” at incredibly small fragments, that analysis yielded a date for the linen rag paper between 1475 and 1640.
The CCI team, including senior conservation scientist Marie-Claude Corbeil, summed up the story as follows: “The results of the tests that were done were conclusive: the painting was executed on wood that dated from the correct period; the materials and the way in which they were used were consistent with a painting done in England in the early 17th century; no anachronistic material was found; and the label identifying the subject of the portrait was made of rag paper dating from 1640 at the latest. All these elements indicated that the painting was indeed an old painting and not a relatively modern copy or fake.”
Five years later, Corbeil still cannot state definitively whether the sitter was Shakespeare, although she points out that the question had not been the institute’s primary goal.
“Our most important contribution was to prove that this painting was from the period,” she says.
What Sullivan calls “the final tests” to date the ink used to write on the paper label affixed to the back of the painting, are being completed by McCrone Associates Inc. in Westmont, Illinois.
(With information from “Scientific Examination of the Sanders Portrait of William Shakespeare,” published in the CCI Newsletter, No. 28, Dec. 2001.)