Experts from Mexico and Costa Rica are working together on the restoration of three ancient Diquís culture limestone spheres now preserved at the Finca 6 Site Museum in Palmar de Osa.

Diquís stone spheres at the National Museum of Costa Rica. These pre-Columbian artifacts from the Diquís Valley are iconic symbols of Costa Rica’s cultural heritage. Credit: Rodtico21 / CC BY-SA 3.0

The project, carried out between July and August, is part of a decade-long heritage conservation collaboration between the National Museum of Costa Rica and Mexico’s National School of Conservation, Restoration, and Museography (ENCRyM).

Over 300 stone spheres, better known as the Diquís Spheres, have been discovered along the Isla del Caño and Diquís Delta. They are part of the extinct Diquís culture, which flourished in southern Costa Rica during the Sinu era (ca. 1500–300 BC). These pre-Columbian artifacts are among the most distinctive symbols of the region’s cultural heritage. Scholars believe they were originally placed in ceremonial plazas or along pathways leading to chiefs’ residences, for both decorative and political purposes.

The three spheres that were treated were initially found at Finca 4, a site renowned for having the highest number of spheres known, arranged in geometric patterns related to nearby structures. These are distinct from most examples, which are usually made from harder igneous rocks, as they are made of conglomerate limestone, a rare and less hardy material choice. The pale stone contains fossilized shells and calcium deposits that soften it and make it vulnerable to environmental conditions.

Diquís stone spheres at the Finca 6 archaeological site. Credit: Axxis10 / CC BY-SA 3.0

The spheres were displayed near a roadside community for years before being moved to the Finca 6 museum. They had fissures, material loss, and surface changes due to exposure to rain, microorganisms, and varying humidity. To counter this, conservators applied a variety of treatments that involved mechanical cleaning, microbial growth removal, and the application of mild bactericides. Delicate areas were supported using lime-based mortars mixed with limestone powder to ensure compatibility with the original stone.

Restoration involved small chromatic adjustments with natural pigments, executed in such a way as to be identifiable and reversible, as per international conservation standards. New bases were constructed to provide stable support, while the spheres are now exhibited under a protective shelter. Their condition is monitored through temperature and humidity controls as part of an extended preventive strategy.

Diquís stone spheres at the National Museum of Costa Rica. These pre-Columbian artifacts from the Diquís Valley are iconic symbols of Costa Rica’s cultural heritage. Credit: WAvegetarian / CC BY-SA 3.0

The binational team is also documenting every detail of the intervention with technical reports and pH๏τographs, building a conservation glossary to be used when standardizing future monitoring. Along with the three limestone spheres, other Diquís artifacts at Finca 6 and other World Heritage sites in the delta are undergoing maintenance.

More information: National Museum of Costa Rica