So, with this experiment concluded....would I use it again? Not sure. While I do love the luminosity, that's achievable with other mediums. The one thing Sergio doesn't reveal in his article is what he uses on the final to back it. I imagine any solid white paper would work. The vellum alone is way too fragile. Of course, under Sergio's masterful hands, this technique produces distinctively glowing illustrations. I can't possibly expect to achieve the same results without his skills and experience.
I am most grateful to artists who are willing to share their process. People like James Gurney, Dan Dos Santos, Donato Giancola, and many others who open the door to their studios and their techniques probably underestimate their value to artist-wanna-be's like myself. It is so helpful. I think with one exception, every artist I've emailed has replied and generously imparted information to me. There are other lesser known artists I follow who post their works in progress and I always gain new knowledge watching them work. My hope is that this meager experiment has been helpful to someone out there. I know I've learned alot. Thanks Sergio!