ski_no = WALL_SKINS_NUMBER
And the REQUEST was not correctly copied (Array-Index) was missing:
x = REQUEST{2} ("Building_Material_info", wand_mat[ii], "gs_bmat_surface", mat_index[ii])
This seems to be prohibited by the forum software (square brackets where left out)
GDL Object Developer
b-prisma
MAC OSx 10.14