UNIVERSITY PARK, Pa. — Glass may look uniform, but some of the strongest and most useful glass materials contain carefully controlled crystals. Their size, number and arrangement can determine whether a material is strong enough for a smartphone screen, transparent enough for an optical device or durable enough for a dental crown.
Scientists still have difficulty observing how those crystals first form. That earliest stage, known as nucleation, influences everything that follows, yet occurs at a scale too small for conventional microscopes to capture. Researchers therefore often rely on repeated experiments to determine which glass compositions and heating conditions will produce the properties they want.
Mason Link, doctoral student in chemical engineering at Penn State, is working to make nucleation easier to understand and predict. By pairing a reexamination of long-standing theory with a method for monitoring crystal formation as it happens, his research could help scientists design glass-ceramics more efficiently and with greater control. The work earned him recognition as Corning’s 2025-26 Glass Age Scholar.
The scholarship provides financial support and a yearlong collaboration with Corning scientists. Link worked with Corning mentors Charlene Smith and Qiang Fu and his Penn State adviser, Seong Kim, to strengthen his experimental design and interpretation. He presented “Toward a Revised Framework for Crystal Nucleation in Glass-Ceramics” at Corning’s virtual Glass Age Scholar mini-symposium on May 27.
“Mason’s work could support stronger display cover glass, transparent windshields for military vehicles, improved dental materials and optical waveguides, which direct light in communications and sensing technologies,” said Kim, head of the Department of Chemical Engineering and Walter L. Robb Family Endowed Chair. “We can facilitate and expedite that kind of research because we will be able to monitor the crystallization process.”
The project draws on Penn State strengths in glass science, computational modeling, surface science and nonlinear optical spectroscopy, according to Kim. It also adapts expertise Kim’s group developed while using related optical methods to study biological materials.
Kim said Link’s choice of topic is part of what distinguishes him as a researcher.
“This is a somewhat old subject. It is not brand new or very fancy, but it is still not fully understood, and the industrial impact is huge,” Kim said. “That is what Mason wants to work on.”
Glass-ceramics are made by intentionally growing crystals within glass to tailor properties such as strength, transparency, durability and heat resistance. Researchers traditionally study nucleation by heating a sample, breaking and chemically etching it, and examining the exposed crystals with electron microscopy. Because each sample offers only one snapshot, the procedure must be repeated under different conditions.
“An entire data set can take months or even years,” Kim said. “It is a very slow, time-consuming process.”
Link is investigating whether second harmonic generation, or SHG, can provide a faster, nondestructive approach. When laser light interacts with certain crystal structures, it produces a detectable signal at twice the original light frequency. That signal could allow researchers to track nuclei as they form and grow while the glass is being heated.
The experiment remains difficult because the nuclei can vary in number, density, size, shape and orientation, with each variable affecting the signal. Those complications led Link to revisit classical nucleation theory, a decades-old framework for describing crystal formation.
Existing approaches can produce conflicting values from the same experimental data, in part because they rely on assumptions such as treating a nucleus as a perfect sphere. Link is testing those assumptions and working to reconcile the approaches, so theoretical predictions better reflect what occurs inside the glass.
Combining better theory with real-time measurement could reduce the trial and error involved in developing glass-ceramics, Kim said.
For Link, the industry collaboration brought a new perspective to the challenges in his work.
“One of the most surprising aspects of this experience was how quickly my mentors were able to identify challenges in my work that I had either overlooked or struggled with,” Link said. “They were often able to provide clear strategies to address those issues, which demonstrated the value of both perspective and experience.”