They are 12-point glass that looks like crystal.  Each knob is 2" across and 1" deep (until it touches brass).  

Together, they're about 6" long, and the brass backplates are 5-1/2" long x 1-1/2" wide at their widest.

This is the only pair I have, though I do have some vintage ceramic doorknobs.

Email me any questions, and check out my other vintage items!