Three limestone spheres, from Finca 4, unique for their mineral composition, are being restored at the Finca 6 Museum Site, in Palmar de Osa, Costa Rica. This work is part of a joint heritage conservation effort initiated by the governments of Costa Rica and Mexico.

As part of a cooperation that has spanned more than a decade, the Museo Nacional de Costa Rica and the National School of Conservation, Restoration and Museography (ENCRyM) of the National Institute of Anthropology and History of Mexico are conducting a conservation-restoration for the three pre-Columbian limestone spheres, also known as Diquís spheres, which were originally found in Finca 4 (a collection of settlements that developed on the alluvial plains of the Sierpe and Térraba rivers). The spheres are now at the Finca 6 Museum Site.

The intervention team consists of restorers from the National Museum, Leifer Castro, Jonathan Zúñiga, and assistant Miguel Rodríguez, with the advising of Mexican archaeologist and restorer Isabel Medina González and Mónica Pinillos, both from ENCRyM.

These pre-Columbian sculptures are especially valuable for being carved in conglomerate limestone, a mineral composition that is uncommon among the Diquís spheres.

“Limestone is a sedimentary rock, which means it was formed from sediments and clasts (fragments of rocks or minerals) compacted and crystallized. In them you can clearly observe some fossil shells and a light color resulting from the large amount of calcium composing the stone, which causes it to be a softer stone than igneous ones — the type of rock with which the majority of spheres are made,” explained Leifer Castro, restorer of the National Museum of Costa Rica.

According to the National Museum of Costa Rica: “These spheres were displayed near the road in a nearby community, then moved to the Finca 6 Museum Site. The vulnerability of the limestone rock and the effects of environmental conditions caused the sculptures to suffer alterations such as water erosion, concretions, loss of material, presence of microorganisms, fissures and weakening.”

The choice of this type of material — rare in the region and complex to work with — suggests that the people who made them carried out a deliberate and precise selection of materials.

These spheres were exposed near the road in a nearby community; later they were moved to the Finca 6 Museum Site. The vulnerability of the limestone and the effects of environmental conditions caused the sculptures to suffer alterations such as erosion,  loss of material, presence of microorganisms, cracks, and weakening.

For their restoration, the team  applied a series of treatments that included mechanical cleaning, elimination of microorganisms, application of mild bactericides, and consolidation using mortars made with lime and mineral aggregates compatible with the original stone.