Does anybody actually use the three plate method with granite? It was originally done with cast iron, and I thought cast iron was still the standard material. The plates are covered with dye and rubbed together to find the high points, which are then scraped off, instead of being removed by the rubbing directly.

Granite is a common material for modern surface plates (and a good one because it doesn't rust and doesn't raise burrs if it's chipped), but I believe these are still made using cast iron reference plates.