Well, it doesn't have to take tons of my time. Most of the equations needed I know already and it's just a matter of choosing parameter values.  You show me the prop, I show you the formula. 

I have dozens of shaders for glass, metal, plastic, paint, wood, china, nylon, leather, cloth, granite, marble, ceramic, clay, mud, blood, water, oil, etc. Assuming you have need of these sorts, they are pretty much instant. It's just a matter of choosing color and shine. Others besides me could try different parameters and show the results.

The tricky stuff is generating procedural patterns - such as the fish scales in my avatar or the chain mail I posted years ago. That takes a while.

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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)