Scientists found these old photographs contain metallic nanoparticles

The earliest reliably dated photograph of people, taken by Louis Daguerre one spring morning in 1838.

Enlarge / The earliest
reliably dated photograph of people, taken by Louis Daguerre one
spring morning in 1838. (credit: Public domain)

Daguerreotypes
are one of the earliest forms of photography, producing images on
silver plates that look subtly different, depending on viewing
angle. For instance they can appear positive or negative, or the
colors can shift from bluish to brownish-red tones. Now an
interdisciplinary team of scientists has discovered that these
unusual optical effects are due to the presence of
metallic nanoparticles
in the plates. They described their
findings in a new
paper
in the Proceedings of the National Academy of
Sciences.

Co-author Alejandro Manjavacas—now at the University of New
Mexico in Albuquerque—was a postdoc at Rice University, which
boasts one of the top nanophotonics research groups in the US.
That’s where he met his co-author, Andrea Schlather, who ended up
in the scientific research department at the Metropolitan Museum of
New York. The Met has a valuable collection of daguerreotypes, and
her new colleagues were keen to find better methods for preserving
these valuable artifacts.

Schlather contacted Manjavacas and suggested this might be a
great place to apply their combined expertise in nanoplasmonics—a
field dedicated to detailing how nanoparticles interact with light.
Think of it this way: light is an optical oscillation made up of
photons. Sound is a mechanical oscillation made up of
quasiparticles known as phonons. And plasma
(ionized gas, the fourth fundamental state of matter) oscillations
consist of plasmons. Surface
plasmons
play a critical role in determining the optical
properties of metals in particular.

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Source: FS – All – Science – News
Scientists found these old photographs contain metallic nanoparticles