Entirely natural  button.
Made from the shell of the coconut, with a slightly textured surface, polished and two holes. 
They are just off-flat, with the concave side and the edge painted with a slightly shiny layer of enamel paint. The convex side is coloured anything from cream to speckled dark brown.
No button is 100% the same due to it being a natural material and therefore they might also have slight imperfections, which adds to its charm.
The buttons are very strong and substantial,  lightweight and washable.