Revealing the Hidden Colors of Prehistoric Shell Ornaments with Raman Spectroscopy

Archaeologists have long known that mollusk shells played an important role in prehistoric societies, often fashioned into ornaments that carried both aesthetic and symbolic meaning. However, because these societies existed long ago, the mollusk shells used during these time periods no longer contain their distinct colors. This is not ideal for archaeologists that are attempting to learn more about these shells and their cultural significance, and the color of these shells could indicate their significance (1). A new study published in Chemosensors sheds light on how Raman spectroscopy combined with computational analysis can help recover these lost details (1).

What are mollusks and why were they important in prehistoric societies?

Mollusks are invertebrate organisms that have existed for thousands of years. As a result, mollusks have an extensive fossil record dating back to the Upper Paleolithic and Mesolithic periods (2). Mollusks were important to older civilizations because their shells were often used as personal adornment. Shell coloration was not just decorative jewelry; it is also probable that there was symbolic and identity-related meaning behind the shells (1). Being able to reconstruct the original colors allows researchers to better understand the choices made by hunter-gatherers and the role these ornaments played in their societies (1).

Fossil Shell Specimen: Close-up of Ancient Marine Life Remains in Sedimentary Rock. Generated with AI. | Image Credit: © png -stock.adobe.com

In their study, the research team studied the shells of Littorina obtusata/fabalis, which was a species widely used as personal adornment during the Upper Paleolithic and Mesolithic periods, spanning approximately 40,000 to 5,000 years ago (1). The team analyzed samples from La Chora cave in Cantabria, northern Spain, using modern specimens as reference points to reconstruct the original coloration of their ancient counterparts (1).

By using Raman spectroscopy with l-means clustering, the researchers were able to classify shell spectra and link archaeological samples to modern shells of known coloration (1). This provided a predictive framework for inferring the likely colors of specimens that had faded because of taphonomic processes over millennia (1).

The researchers also discovered through their analysis that even when surface colors are no longer visible, pigment-related spectral features persist within shell layers. By examining polished cross-sections, the researchers uncovered non-uniform pigment distributions, suggesting that coloration extended beyond surface appearances (1). This discovery enhances the understanding of both the biology of mollusks and the cultural significance of shell selection in prehistory (1).

What are the key takeaways from this study?

The main takeaway from this study is that prehistoric people may have deliberately chosen shells based on specific aesthetic traits. Given the considerable variation in coloration and patterning within a single species, the ability to reconstruct original hues supports the hypothesis that ornament choice was influenced by color preference, potentially tied to group identity, symbolism, or aesthetic appeal (1).

Another important takeaway is that the researchers proposed a framework that could be applied to other biomineralized structures. As a result, their method could potentially be applied to conservation science and cultural heritage research (1).

What were the limitations of this study?

There were a few important limitations in this study. For one, the research team had to define the number of clusters in advance because they used the k-means clustering algorithm. The issue is that by doing this, the researchers unintentionally may have influenced results and lead to sensitivity in initialization (1). The authors suggested in their study that alternative clustering approaches, such as agglomerative hierarchical clustering (AHC) or density-based spatial clustering of applications with noise (DBSCAN), could complement or refine the methodology (1).

Despite these limitations, the study marks a significant advance in archaeological science. By bridging spectroscopy and computational modeling, the researchers provide a new means of reviving lost visual information, which in turn deepens our understanding of prehistoric cultural practices (1).

References

1. Perez-Asensio, A.; Fernandez-Manteca, M. G.; Cuenca-Solana, D.; et al. Predicting the Color of Archaeological Littorina obtusata/fabalis Shells Using Raman Spectroscopy and Clustering Algorithms. Chemosensors 2025, 13 (7), 232. DOI: 10.3390/chemosensors13070232
2. Wanninger, A.; Wollesen, T. The Evolution of Molluscs. Biol. Rev. Camb. Philos. Soc. 2018, 94 (1), 102–115. DOI: 10.1111/brv.12439