I found 2 candle holders in an antique shop that I at first thought were just metal because of the price and the silver color. I then looked at the bottom and found no engravings and noticed that it looked like brass on the bottom, then noticed the complete holders had brass showing through in areas. I need to know, how long does it take for brass to tarnish to a silver color, and to become so densly covered. It's passed the magnet test. Thank You, Luther Keene