How to render one side of a cube with different material than the other sides Picking up 3D graphics since 2004, so I'm a bit lost now.

I'm trying to make a cube of metal look rough cut on 5 sides, and mirror smooth on one side.

I've managed to control the roughness with vectors for the bumb and so on, but I hit the wall trying to assign another property of the one side to be smooth.

I'm thinking it should just be to separate the face that are to be smooth from the rest.

When looking into this site's answers, it looks like I just have to select the face I want to separate with key "Y". It's separates all right, but I can't seem to assign a specific material to that separated side, it always includes the other sides vectored bump.

Why is a separated mesh face still "slaved" to the other faces when it comes to material assignment?
"You do not, and should not, separate a face if all you want is to assign a different material to it. You just add another material in the materials tab, make sure it is highlighted, tab into edit mode, select the face(s) you want and click the 'assign' button. – photox 2 hours ago"