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 cream in colour and the slightly convex side 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.