1. A method for material classification of a specular sample fabricated from an unknown material, the method comprising: obtaining a measurement of a specular reflection of the sample at at least one observation angle and in at least two spectral bands including a first spectral band and a second spectral band; calculating a feature vector using a homogeneous function that combines the measured specular reflections in the first and second spectral bands; and classifying the sample based on the feature vector; wherein the homogeneous function includes a ratio of values of the first and second spectral bands of the measured specular reflections, and wherein the feature vector is based on a histogram of ratio values of the first and second spectral bands of the measured specular reflections.