If the appropriate processes are used, wood can be curved and remain in the desired shape - and for this, there is a number of known techniques which Australian company, Sculptform, has perfected.

The positive curvature is convex rather than concave ... is described as being open and negatively curved, like the concave shape of a saddle, and quite possibly infinite in extent.

In a ray diagram, a concave lens is drawn as a vertical line with inward facing arrows to indicate the shape of the lens.

Optical Surfaces Ltd. is a leading international supplier of concave and convex spherical mirrors made to your exact specification. A spherical mirror is a mirror which has the shape of a piece cut ...

These lenses are either convex - converging light, which magnifies an object, or concave, where light diverges making an object smaller. However, this new lens is 40 nm thin on a flat glass surface .