These bottles constitute
extraordinary examples of aesthetic criteria: the concave
and the convex acquire a complimentary quality, and the
very stylized forms propitiate an image of great harmony,
achieved in the wake of a work of excellent artistic quality.

The description above is from the display at the museum.
The display is “titled”;
Bottles Concave and convex
Cupisnique Formative Period 1250 B.C. – 1 A.D.