Scientists analyse Darwin’s Original Specimens Without Opening 200-Year-Old Jars

The study examined 46 historic specimens at the Natural History Museum, London, including mammals, reptiles, fish, jellyfish, and shrimps collected by Darwin and other naturalists.

It was found that traditional preservation methods differed by species and era: mammals and reptiles were typically fixed in formalin and stored in ethanol, while invertebrates might be kept in formalin, buffered solutions, or mixtures containing additives like glycerol. 

The achievement addresses a long-standing challenge for museums worldwide: how to monitor the condition of preserved specimens without exposing them to contamination, evaporation, or environmental damage that comes from opening their containers.

For collection curators, knowing the exact composition of these fluids is essential for monitoring specimen condition.

“Until now, understanding what preservation fluid is in each jar meant opening them, which risks evaporation, contamination, and exposing specimens to environmental damage,” says Dr Sara Mosca, STFC Central Laser Facility. “This technique allows us to monitor and care for these invaluable specimens without compromising their integrity.”  

The researchers used a portable laser spectroscopy method called Spatially Offset Raman Spectroscopy (SORS) to peer through glass and identify the chemical composition of preservation fluids.

SORS performs chemical analysis by shining a laser light into a container and inspecting the changes in wavelength that occur when the light is reflected. These changes indicate the presence of different chemical components within it.

SORS, originally developed at STFC’s Central Laser Facility, is the same technique which is used in airport scanners all over the world through Agilent Technologies.

The technique correctly identified fluids in approximately 80% of cases tested, with partial identification in another 15%. It also determined the types of glass or plastic containers used, providing insights into how storage methods have evolved over time.

With over 100 million fluid-preserved specimens housed in museums worldwide, the ability to analyse preservation fluids non-invasively offers conservators and curators a new tool for monitoring collection health and intervening before problems arise.

The research was conducted by a collaboration between the Science and Technology Facilities Council, the Natural History Museum and Agilent Technologies.

“As part of NHM Unlocked, here at the Museum we can analyse jars containing specimens without opening and disturbing their integrity,” says Wren Montgomery, research technician at the Natural History Museum. “This work is the next step in demonstrating the Museum’s commitment to transforming the study of natural history.  Analysing the storage conditions of precious specimens, and understanding the fluid in which they are kept, could have huge implications for how we care for collections and preserve them for future research for years to come.”

The study has been published in ACS Omega and featured as the ACS Editors\' Choice on 13 January, 2025, and can be found here: https://pubs.acs.org/doi/10.1021/acsomega.5c09045 

Image: Specimens preserved in jars at the Natural History Museum. Credit: Sara Mosca, STFC Central Laser Facility