Integration of the NIST Spectroscopic Plate Archive into the Harvard Plate Stacks

For more than a century, scientists have captured the light of stars and the glow of hot gases on sheets of glass coated with a light-sensitive chemical. These glass plates, dark and heavy, act as a permanent record of the universe's fingerprint. When an element is heated, it emits light at very specific colors, creating a unique pattern of lines that tells researchers exactly what that element is and how it behaves. By studying these patterns, astronomers can determine the composition of distant stars, while physicists use the same data to understand the fundamental structure of matter itself. For decades, a vast library of these glass records sat quietly in a government laboratory, waiting for someone to look at them again with fresh eyes and modern tools.

In March 2025, the National Institute of Standards and Technology (NIST) closed its atomic spectroscopy group, leaving behind a collection of thousands of these photographic glass plates that could not be replaced. Rather than letting this history disappear, staff from the Harvard Plate Stacks at the Center for Astrophysics stepped in to take custody of the archive. The Harvard Plate Stacks is already the largest collection of its kind in the world, holding over half a million glass plates dating from the 1880s to the 1990s. When the NIST collection arrived in Cambridge in the spring of 2025, it joined a massive repository of scientific history. Researchers Jacob Ward and Gillian Nave began the work of sorting through the new arrivals, discovering that many of the plates held scientific value that had been overlooked or only partially explored.

The collection is a mix of records from different institutions, including the Massachusetts Institute of Technology and the University of California, Berkeley, but the majority came from instruments at NIST and its predecessor, the National Bureau of Standards. The plates capture spectra from a wide range of elements, from the simplest to the most complex. Some were taken to study neutral atoms, while others captured light from atoms that had been stripped of several electrons. Among the most interesting finds were plates of cerium, an element currently vital for understanding the explosive collisions of neutron stars known as kilonovae. Although scientists had derived energy levels from these cerium plates years ago, the detailed lists of spectral lines had never been published. Similarly, the archive holds plates of zirconium and other heavy elements that were only partially analyzed, leaving a wealth of data waiting to be fully unlocked.

Preserving these fragile objects is a race against time. The researchers found that the way the plates were stored in the past had sometimes caused more harm than good. Many were kept in plastic sleeves that, over decades, began to break down and release a gas that smelled like vinegar. This gas reacted with the photographic coating, turning it yellow and causing the emulsion to flake off the glass. In contrast, some plates stored in simple paper boxes, though not ideal, had fared better because they were not trapped in a humid, chemical-filled environment. The team now faces the task of moving every single plate into special acid-free paper sleeves and metal cabinets designed to keep them safe for decades to come. Before this work can begin, the team must carefully photograph the plates while they are still in their damaged sleeves to capture any handwritten notes or flaking details that might be lost once the plastic is removed.

To make this data useful for modern science, the team is digitizing the plates using high-resolution scanners. They are also scanning the laboratory notebooks that accompanied the plates, which contain the original measurements and dates. These notebooks are crucial for linking the physical glass to the data it holds. The goal is to create a complete, searchable digital archive that scientists around the world can access. While the team does not yet have the resources to scan every single plate immediately, they are prioritizing those that are most likely to yield new discoveries. They are also working to digitize the lab books, which will help them organize the collection and understand exactly what each plate contains.

The value of this effort was demonstrated when the team re-examined a single plate of zirconium spectra that had been taken at MIT in the 1930s. By rescanning the plate with modern equipment and comparing the results against current standards, they were able to measure the wavelengths of the light with far greater precision than was possible when the plate was first created. The new measurements reduced the uncertainty in the data by a factor of four, proving that even old records can provide better answers when viewed with new technology. This single example suggests that the thousands of other plates in the archive could offer similar improvements to our understanding of atomic physics.

The future of this collection depends on collaboration and funding. The team at Harvard has the expertise and the equipment to handle the plates, but scanning thousands of glass negatives is a massive undertaking that requires dedicated staff and financial support. They are open to working with the broader scientific community to identify which plates are most urgent to digitize. For now, the priority is to finish the initial inventory, rehouse the plates to stop further decay, and make the existing digital records available. The archive represents a bridge between the past and the future, preserving the work of generations of scientists while offering a chance to refine our understanding of the universe with the tools of today.