// Here's the bit of material.cpp that changed:

const Material Material::zero( vec3( 0.0, 0.0, 0.0 ),
                         vec3( 0.0, 0.0, 0.0 ),
                         vec3( 0.0, 0.0, 0.0 ),
                         vec3( 0.0, 0.0, 0.0 ),
                         0.0, 0.0 );