An important problem in robot vision is to be able to recognize metal objects. The task is made difficult because of specularities and interreflections. Machined surfaces often have different reflectance properties in different directions due to structures created by the machining process. It is often impossible to describe the reflectance using a simple reflectance function. Therefore, it is important to learn more about the reflective properties of machined metal surfaces to foresee and deal with them. The optical behavior of machined surfaces is studied. Machining operations are considered geometrically, mechanically, optically, and at the microstructure level. The conclusions are that the reflection properties of machined surfaces must be divided into two functions, one parallel to the machining direction, which is likely to be Gaussian distributed, and one perpendicular to the structure, which should be considered as a signature of the machining process and will vary accordingly. The position of the maximum intensity perpendicular to the parallel reflection is, however, very predictable, and an experiment is discussed that illustrates how specular reflections caused by point source illuminators can be used to estimate surface shape. The experiment also verifies the suggested reflection model.