Hi, Johnatan! Thanks for lessons!
When I unload the model, the materials are not displayed. I've tried different ways and different versions of blender. I've using sketchfab-exporter for blender 2.7x. I've tried different types of exported files, using archive for obj + mtl, but nothing. Help from Sketchfab and searching from google did not bring results.
Hey Sergey! The submission for this exercise is an image, so you don't need to export to Sketchfab FYI. Material slots transfer with your file to other programs (the name and which faces they are assigned to), but not the shader properties themselves because no two render engines are the same. Hope that helps!