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Although, I haven't tried it, one can add limestone crushed or sand to concrete to make "marble". It can then be polished.
A variation on wax paper is to use aluminum foil. In my house it is always available, not so much wax paper.
I built this and I am impressed. It works great, and is omnidirectional. I had a problem pushing the copper tubing through the holes. I would suggest, at additional expense, to drill holes through pvc couplings and then put the tubing through those holes and bend and glue couplings to "star" pipes. I wish I had thought of that before I made mine. All in all agreat easy project that works great!