Really? Glass knobs were never used in bathrooms until the advent of the vanity in the Post WWII era. Although I did have a linen cabinet in a 1914 bath once....it did have a glass knob. But then so did the kitchen. Cabinets in either area are a relatively new phenomenon. If you like the knobs in glass, do it. Like this?

http://www.pullsdirect.com/emtek-86011-old-town-1-1-4-clear-crystal-cabinet-knob-with-solid-brass-rosette/p473389