/usr/share/gwyddion/glmaterials/Polished-Copper is in gwyddion-common 2.44-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | Gwyddion resource GwyGLMaterial
0.2295 0.08825 0.0275 1.0
0.5508 0.2118 0.066 1.0
0.580594 0.223257 0.0695701 1.0
0.0 0.0 0.0 1.0
0.4
|