Note - The Old cube code now sits inside of the oldGLCube branch.
The Normals for circular plate of the down face is slightly inaccurate which gives weird lighting glow in the GL application. I corrected the normals for up face of the circular plate model in Blender and the updated model is present in output/models/Teapot.
I added material textures for Teapot and Principled BSDF material for other meshes. The new teapot_n_glassMAT blender file has the updated model. This Teapot render is missing roughness map, normal map and the metallic map.