i have seen this lamp before, i like it a lot, and belive it or not i was planning to do a render of it too, hehehe.. i think you are making it very good, about the dark glass maybe change some settings in the difuse layer or on the skp model.
Great job cucullan yoiu have done a great aproach of this intresting design lamps. keep it up and great job, and for the plastic material the one you have its ok but for very results add more subdivision. keep it up!