While at work today I was lamenting about the price of marble and how I couldn't find a properly sized small slab so that I could try my hand at lapping film. My coworker asked why I needed a marble slab? I replied I needed a hard, perfecftly smooth, flat surface on which to affix the film. He looks at me puzzled, and goes "Dude, you're a machinist!" and points to the mountain of scrap steel slabs. Aha! Twenty minutes later I had my 3"x10" lapped steel surface. Sometimes the obvious escapes me.