Caves may not get great natural light, but a low-ceilinged one in Ethiopia represents one of the earliest known and longest-running art workshops. According to a new study by a group of European archaeologists, published in the journal PLOS ONE, the 40,000-year-old Porc-Epic Cave in eastern Ethiopia served as a site for the continuous production of ochre powder — which prehistoric people often used for paint — for at least 4,500 years. Over that time, cave dwellers built up a nearly 90-pound cache of the reddish, iron-rich rocks, the largest known East African ochre assemblage from the Middle Stone Age.

“Considering the large amount of ochre processed at the site, this continuity can be interpreted as the expression of a cohesive cultural adaptation, largely shared by all community members and consistently transmitted through time,” the researchers write. In other words, the site functioned similarly to a modern-day paint workshop, as a center where ochre was imported in large slabs or small pieces, then hand-ground into fine powder. Researchers even found particular rock pieces that may indicate the work of apprentices who were training to properly flake and grind the raw material. The findings resemble those from another cave in South Africa, a 100,000-year-old site where humans processed ochre and stored it in abalone shells.

In the case of the younger Porc-Epic, archaeologists examined about 4,000 pieces of ochre — now all housed at the National Museum of Ethiopia — as well as a number of ochre-processing tools and ochre-stained artifacts, to understand how humans transformed the naturally occurring substance into a valuable tool for their community. The researchers also ground up some ochre themselves, experimenting with different stones and analyzing the results. What they found was that myriad shades and powders of varying coarseness could be produced from the material, from yellow and oranges to reds and grays.

The pigment was used for a variety of purposes, but samples were likely made mostly for “symbolic activities,” the researchers write, such as cave or body painting; some ochre pieces even appear to be ground to a point at one end, as if they were once used like crayons. Another notable find: a round pebble half-covered with ochre that suggests use as a stamp to apply pigments to or even form patterns on soft material.

It is possible that some powders served more functional purposes. People may have used them to tan animal hides or applied them to their skin as an early form of sunblock or insect repellent, the study explains. What’s certain, though, is that Porc-Epic remained a busy site of ochre processing for over four millennia, evidently catering to communities that relied on the expertise of generations of artisans.