There's no great magic to airbrushing. If you can learn to use a mill from scratch, the airbrush won't hold any mysteries. There are a few good instructional videos on DVD and on YouTube. The Knowledge Base has some thoughts about selecting an airbrush here:
http://www.armortek.co.uk/Forum3b/viewt ... f=2&t=5506
Final thought. The interior of the episcopes presents a challenge. I'm really not sure about the best coating to use. They certainly shouldn't remain in natural metal. The real ones had a dark anti-reflecting coating as seen here:


Looking forward to the next installment.
Regards.
Stephen