Volume scattering is a phenomenon that occurs in an optical medium (e.g., glass or plastic), where the presence of small particles within the volume of the material causes light to scatter. Particulate flaws in the medium may occur due to small bubbles, inclusions, or contamination. Scatter from these sources is similar in nature to that from surface particulates except that it cannot be eliminated by cleaning. The particles within such an optical medium generally scatter light in both forward and backward directions. The scattered intensity and polarization are not easily related to defect characteristics, and there is no minimum scatter angle associated with the illuminated spot size, as is found with surface scatter.