By Maziar Montazerian, John C. Mauro, and Andréa S.S. de Camargo

Austrian chemist Richard A. Zsigmondy was known for his work in colloid chemistry, but his research inspired advancements in optical glasses as well.

Although few Nobel Prizes have been awarded for research in glass science, glass has played a critical role in enabling Nobel-winning discoveries. For example, optical glasses are critical components for seeing both the microscopic world and the greater cosmos, enabling the entire fields of microbiology and modern astronomy.

The sole Nobel Prize recognizing optical glasses was awarded to Charles Kao in 2009 for “groundbreaking achievements concerning the transmission of light in fibers for optical communication,” an idea that was reduced to practice by Donald Keck, Robert Maurer, and Peter Schultz at Corning Glass Works (Corning, N.Y.).¹ What is less known is that one of the early winners of the Nobel Prize in Chemistry (1925), Austrian chemist Richard A. Zsigmondy (1865–1929), was also a pioneer in optical glasses because of his work in colloid chemistry.²

Zsigmondy was born in Vienna, Austria, on April 1, 1865. He was influenced by the chemistry textbooks of Roscoe-Schorlemmer and Berzelius during his youth. Under the mentorship of professor E. Ludwig from the Medical Faculty in Vienna, he gained basic knowledge in quantitative chemical analysis.

Zsigmondy first studied at the Technische Hochschule in Vienna and then moved to Germany in 1887 to study organic chemistry at the University of Munich under professor W. von Miller. In 1889, he was awarded a doctorate in organic chemistry and remained Miller’s assistant until 1891.²

From 1891 to 1892, Zsigmondy assisted professor August Kundt at the University of Berlin, and this experience led him to develop a strong interest in inorganic chemistry, specifically the luster colors derived from gold particles in porcelain. After joining the Technische Hochschule in Graz as lecturer, Zsigmondy continued investigating how fine gold particles can impart color to materials, this time in the context of gold ruby glass.

Gold ruby or “cranberry” glass is created by adding gold salts, typically in the form of gold chloride, to otherwise colorless molten glass. The salt is then reduced to gold nanoparticles via the addition of metallic tin to obtain a red color.³

During the late 19^th century, the nature of this colloidal gold solution was not well understood, so Zsigmondy aimed to elucidate this behavior. These investigations allowed Zsigmondy to gain knowledge of glass and proficiency in producing colored glass, and this expertise brought him to employment at SCHOTT in Jena, Germany, in 1897.

After joining SCHOTT, Zsigmondy continued his studies of colloidal solutions and was responsible for the development of the well-known Jena milk glass, a type of opaque or semi-opaque glass with a white or milky appearance. However, he left SCHOTT in 1900 to focus his scientific efforts on studying colloid chemistry.

In early experiments, Zsigmondy used a glass cube containing dispersed gold colloidal particles as his sample. Sunlight served as the illumination source, and a heliostat was employed to compensate for the movement of the sun relative to the Earth. A glass lens was used to focus the sunlight onto a very small area within the glass cube. The glass cube was then examined using a standard upright light microscope. To ensure that no direct illumination light entered the microscope’s optical axis, the optical axis was kept perpendicular to the axis of illumination. Through this setup, Zsigmondy observed the cone of light created by scattering from individual colloidal particles.

Expanding on this setup, Zsigmondy created the concept of the ultramicroscope, a tool that allows for the visualization of particles far smaller than what can be seen using regular optical microscopes. In the ultramicroscope, illumination of samples is done sideways, which allows the light to be scattered rather than simply reflected. This scattering makes the otherwise invisible particles appear as bright points of light against a dark background, allowing for their observation and study even when the particles are smaller than the wavelength of light.^4–7

Zsigmondy collaborated with physicist Henry F.W. Siedentopf (1872–1940) to develop the ultramicroscope, a process which was facilitated by progress in optical glass at that time. He experimented with this device using different colloids and eventually developed a method for measuring the size of ultramicroscopic colloidal particles, such as the gold nanoparticles in gold ruby glass. This research not only allowed him to explain how particle size influences color and how colloids function, but it also made a significant contribution to the wider domain of materials science, where the meticulous manipulation of material characteristics is crucial for fostering innovation.

As a result of his significant contributions to colloid chemistry, Zsigmondy was awarded the Nobel Prize in Chemistry in 1925. But this research had a lasting impact on glass science as well by catalyzing future advancements in optical technologies, which subsequently influenced later Nobel Prize-winning discoveries. For example, the 2023 Nobel Prize in Chemistry was awarded to Bawendi, Ekimov, and Brus for the discovery and synthesis of quantum dots. Key to this discovery was the ability to observe size-dependent optical effects in glass using nanoscale imaging technologies.⁸

Today, there is significant interest in developing glass-ceramics, particularly in fiber form, that incorporate crystalline phases ranging from quantum dots to nanocrystals for use as gas and chemical sensors. Other glass-ceramic forms, such as films and coatings, are being explored to enhance solar energy harvesting and conversion in photovoltaic cells, solar concentrators, white LED devices, and displays in general. Additionally, glasses containing gold and silver nanoparticles are extensively studied for surface-enhanced Raman scattering and the plasmonic enhancement of emissions from rare earth and other transition metal ions.^9,10 In this context, it is fair to state that Zsigmondy’s work was pioneering in these directions.

Other recipients of the Nobel Prize have produced notable advancements in the field of glass research as well, albeit sometimes indirectly. One example is Sir William Ramsay, the recipient of the 1904 Nobel Prize in Chemistry for his discovery of noble gases. He made contributions to the comprehension of gas behavior in glass, which is essential for applications such as vacuum tubes and gas-discharge lamps. His studies were conducted in blown glass apparatuses that he created himself, a skill he learned from his assistant Sydney Young (who was later elected a Fellow of the Royal Society).¹¹ The main applications of optical glass resulting from Zsigmondy’s and others’ endeavors are illustrated in Figure 1.

Zsigmondy’s contributions illustrate that even during the early 20^th century, fundamental glass research could result in the greatest accolades in the field of science. It also emphasizes the crucial significance of glass in facilitating innovative research and technological progress.

In the future, researchers will likely continue building upon Zsigmondy’s pioneering work with the development of ultralow-loss glass fibers for quantum communication, next-generation laser glasses, optical glasses for long-term three-dimensional memory storage, and specialty glass lenses for augmented reality applications. And who knows? One of these developments may very well become the next Nobel Prize-winning discovery.

About the authors
Maziar Montazerian is assistant research professor of materials science and engineering at The Pennsylvania State University. John C. Mauro is the Dorothy Pate Enright Professor of materials science and engineering at The Pennsylvania State University. Andréa S.S. de Camargo is professor at Friedrich-Schiller University Jena, Germany, and head of Division 5.6–Glass, at the Federal Institute for Materials Research and Testing in Berlin, Germany. Contact Montazerian.