I am a big fan of two pen makers/casters - Mark Dreyer and John Underhill - Mark being more about turning and finishing, and John is a premier blank caster.
Mark has a great series on You Tube "10 Minutes to Better Pen Making' and he just introduced a new video for the series. This video is a joint effort by both Mark and John about specialty casting for pen blanks. Their videos are really excellent, and I highly recommend taking a look.
Enjoy!
Kevin Seiler
Link Watch on YouTube