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A particle accelerator is revealing the people in 150-year-old photographs whose features had been lost to time, Science News reports.

For the first time, Madalena Kozachuk, a Ph.D. candidate at Canada’s Western University, and a team of scientists used an accelerator called a synchrotron to scan daguerreotypes, an ancestor of modern photography.

Invented by French painter and physicist Louis Daguerre, daguerreotypes were popular from around the 1840s to the 1860s. They were created by exposing an iodized silver-coated copper plate to a camera (the iodine helped make the plate’s surface light-sensitive). Subjects had to sit in front of the camera for 20 to 30 minutes to set the portrait, down from the eight hours it took before Daguerre perfected his method. Photographers could then develop and fix the image with a combination of mercury and table salt.

Because they’re made of metal, though, daguerreotypes are prone to tarnish. Scientists can sometimes recover historical daguerreotypes by analyzing samples taken from their surface, but such attempts are often both destructive and futile, Kozachuk wrote in a study published in Scientific Reports.

Kozachuk found that using a particle accelerator is a less invasive and more accurate method. While some scientists have used X-ray imaging machines to digitally scan other historical objects, such instruments are too large to scan daguerreotypes. Reading the subtle variations on a daguerreotype surface requires a micron-level beam that only a particle accelerator can currently produce. By tracing the pattern of mercury deposits in the tarnished plate, the researchers were able to reveal the obscured image and create a digital photo of what the daguerrotype looked like when it was first made.

“When the image became apparent, it was jaw-dropping,” Kozachuk told Science News. “I squealed when the first face popped up.”

Scanning one square centimeter of each 8-by-7 centimeter plate took about eight hours. The technique, though time-intensive, may allow museums and collectors to restore old daguerreotypes with minimal damage.

“The ability to recover lost images will enable museums to expand their understanding of daguerreotype collections, as severely degraded plates would not otherwise have been able to be studied or viewed by interested scholars,” Kozachuk wrote.

[h/t Science News]

This article originally appeared here via Google News