I have a house in Massachusetts that was built in 1900. All of the doors and moldings are original, and the interior knobs also appear original (or at least quite old). We have mostly white porcelain knobs, but there are a few black porcelain knobs on closet doors (but not all of the closet doors). I know white porcelain were common at the turn of the century, but are the black also original to the time period? Why would there be only a few doors with black, without any apparent pattern? Thanks!