# like polished bronze, like bronze that had been refined in a furnace

"like bronze that has been purified in a hot furnace and polished" 

# furnace

a strong container for holding a very hot fire. People would put metal in it, and the hot fire would burn away any impurities that were in the metal.

# the sound of many rushing waters

This is very loud, like the sound of a large, fast flowing river, of a large waterfall, or of loud waves in the sea.