The nature photographer Christopher Burkett uses masking to control the printing of his 8x10 transparancies. He gives a brief overview of his process in his new book (Intimations of Paradise), but he does not go into much detail. He does say that he uses as many as five masks to print a single image. I've seen his 30x40 prints in galleries and they are the best I've ever seen. In his book he also says that he spends 2 months a year photographing and 10 months printing -- so I don't think it's a quick and easy process.