Rembrandt's "Night Watch" painted in 1642 has a misleading title. It depicts a militia on patrol, but the background is clearly daytime, not nighttime. The overall darkness of the painting along with the brightly painted center gives the impression of a night scene. This may have led to the title being assigned as such a century later.
There is another reason it can easily be mistaken for a night scene: the chemical reaction of the paint. Rembrandt used a lot of lead-based paints, with lead white being a representative example. Lead in the paint turns black when it comes into contact with sulfur. Over time, the night in "Night Watch" has gradually deepened.
A deep-sea creature that creates toxic paints has been discovered. A research team led by Dr. Chaolun Li from the Institute of Oceanology, Chinese Academy of Sciences, noted on the 26th in the international journal "PLOS Biology" that "polychaetes living in deep-sea hydrothermal vents, where hot water is expelled, were confirmed to combine toxic arsenic and sulfur in their cells."
◇Poison is governed by poison
Polychaetes refer to annelids with thick bristles, like earthworms or centipedes. The research team collected a polychaete known as "Paralvinella hessleri" from a deep-sea hydrothermal vent near Okinawa, Japan using a remotely operated vehicle (ROV). They confirmed that sulfur and arsenic account for more than 1% of the body weight in tissues and organs of Paralvinella.
When seawater seeps through broken cracks in the ocean floor and encounters molten magma at enormous temperatures, it melts the surrounding minerals. The hot water expelled from hydrothermal vents, shaped like chimneys at a height of 30 meters, contains many dissolved minerals. Toxic sulfides and arsenic are typical. Both are toxic substances, but the deep-sea worms are unaffected due to a strategy of governing poison with poison.
Analysis revealed that the deep-sea worms first accumulate arsenic particles and then react them with sulfides to produce less harmful yellow mineral particles known as arsenic trisulfide (As₂S₃). This is a biomineralization reaction that creates minerals within their bodies. Dr. Hao Wang, the lead author of the paper, said, "The bright yellow Paralvinella hessleri stood out distinctly against the dark hydrothermal vent background on the ROV monitor."
Arsenic trisulfide has been a favored substance for paints from ancient times to the 19th century. Ancient Egyptian artists mixed arsenic trisulfide with indigo to create a deep green color. Renaissance painters like Titian and Raphael used arsenic trisulfide to achieve a golden hue in their paintings. The same goes for Rembrandt in the Baroque period. Researchers at the Delft University of Technology in the Netherlands discovered orpiment, a component used for yellow or orange pigments, in Rembrandt's 1665 work "Jewish Couple."
Dr. Hao Wang noted, "What makes this discovery even more interesting is that this creature produces a toxic golden mineral known as orpiment, which was used as a valuable pigment by artists in the Middle Ages and the Renaissance," adding, "It was a fascinating intersection of biology and art history in the depths of the sea."
◇Deep-sea creatures armored with toxic substances
Arsenic trisulfide is highly toxic and is no longer used in paints. Deep-sea worms were also using it for purposes other than painting. The arsenic particles neutralizing poison surround the worms like armor, protecting them from the toxic environment, the researchers stated.
Previously, other deep-sea creatures using a similar method for protection have been discovered. The scaly-foot gastropod (Chrysomallon squamiferum), first discovered in 2003, lives in hydrothermal vents at a depth of 2,900 meters in the Indian Ocean. This gastropod has pieces of metal embedded beneath its shell, resembling the iron throne from the American TV series "Game of Thrones." The gastropod creates armor that defeats competitors and predators by detoxifying toxic sulfides while combining iron and sulfur.
Researchers from Japan and Ireland noted in 2019 in the international journal "Nature Ecology & Evolution" that snails covered in iron armor are also facing extinction due to deep-sea mineral mining, making protective measures urgent. The scaly-foot gastropod has become endangered because economically valuable minerals like copper, iron, lead, zinc, gold, and silver are often found combined with sulfur around hydrothermal vent areas. Water that has melted minerals underground is expelled through the vents and cools, resulting in mineral deposits that can be mined.
Deep-sea minerals are found in various locations. In the abyssal plains at a depth of 4,000 meters, metal nodules the size of potatoes are scattered. These nodules contain a lot of copper, nickel, and manganese. Seamounts are covered with crust rich in cobalt. Hydrothermal vents in the deep sea are abundant in copper sulfides and iron sulfides. Along with these, many unique creatures not often seen on land or in shallow waters also reside.
The United Nations has declared the deep seabed as "the common heritage of mankind." However, no matter how armored deep-sea creatures are, they cannot withstand human intervention. In 2019, the International Union for Conservation of Nature (IUCN) announced that the scaly-foot gastropod was the first animal driven to the brink of extinction due to deep-sea mineral mining. Who will become the knight to protect the deep-sea creatures?
References
PLoS Biology(2025), DOI: https://doi.org/10.1371/journal.pbio.3003291
npj Heritage Science(2025), DOI: https://doi.org/10.1038/s40494-025-01874-w
Nature Ecology & Evolution(2019), DOI: https://doi.org/10.1038/s41559-019-0930-2
npj Heritage Science(2017), DOI: https://doi.org/10.1186/s40494-017-0138-1