Use the Grouping Tool, select individual polygons, click the Assign Material button, choose an existing one or create a new material by name. This lets you associate material names with individual or groups of polygons.

Once a material name is defined, you can load shaders into that material in the material room, or drag and drop onto the polygon that now belongs with that material.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)