Art curators will be able to recover images on daguerreotypes, the earliest form of photography that used silver plates, after a team of scientists led by Western University learned how to use light to see through degradation that has occurred over time.

Research published in Scientific Reports – Nature includes two images from the National Gallery of Canada’s photography research unit that show photographs that were taken, perhaps as early as 1850, but were no longer visible because of tarnish and other damage. The retrieved images, one of a woman and the other of a man, were beyond recognition.

“The image is totally unexpected because you don’t see it on the plate at all. It’s hidden behind time,” said Madalena Kozachuk, lead author of the paper in Western’s Department of Chemistry. “But then we see it and we can see such fine details: the eyes, the folds of the clothing, the detailed embroidered patterns of the table cloth.”

Invented in 1839, daguerreotype images were created using a highly polished silver-coated copper plate that was sensitive to light when exposed to an iodine vapour. Subjects had to pose without moving for two to three minutes for the image to imprint on the plate, which was then developed as a photograph using a mercury vapour that was heated.

Kozachuk used rapid-scanning micro-X-ray fluorescence imaging to analyse the plates, which are about 7.5 cm wide, and identified where mercury was distributed on the plates. With an X-ray beam as small as 10×10 microns (a human scalp hair averages 75 microns across) and at an energy most sensitive to mercury absorption, the scan of each daguerreotype took about eight hours.

This research will contribute to improving how daguerreotype images are recovered when cleaning is possible and will provide a way to seeing what’s below the tarnish if cleaning is not possible.

As the first commercialised photographic process, the daguerreotype is thought to be the first “true” visual representation of history. Unlike painters who could use “poetic licence” in their work, the daguerreotype reflected precisely what was photographed.

Millions of daguerreotypes were created over 20 years in the 19th century before the process was replaced. By improving the process of restoring these centuries-old images, the scientists are contributing to the historical record. What was thought to be lost that showed the life and times of people from the 19th century can now be found.