I have to ask: how did you do the segmentation on the beautiful pen??? Philip
First make sure the blank is perfectly square. Then using a disk sander and a miter gauge set to 45 degrees, sand all 4 sides until you have a point. Then glue a piece of flashing and your contrasting wood to one side. Go back and sand it flush to the long sides of the pen and flush to the point. Next to the side opposite the first side or your scallops won't work out. After that do the same thing to the other 2 sides. Chuck it in the lathe and drill it out, glue in the tube and turn as normal.
A few hints:
Be sure to scuff the aluminum flashing with 100 grit sandpaper on both sides so the glue has a tooth to stick to.
The blank has to be 100% square for this to work right. I rough it with a table saw and then use the disk sander to get everything square.
I don't go so far as using digital calipers, just my grandfathers old brass calipers like this. As long as it slides the length of the blank on both axis (axises, axis' axi?), it's square enough for me.
After I do the fountain pen, I'm going to experiment with veneer sandwiches in lieu of aluminum flashing. I'm working on an 1880 house and have some of the original wood from putting in exhaust fans. I'm going to use those for the scallops and wood from a 150 year old oak from down the street for his pen and cherry for hers. I'll use a dark/light/dark veneer sandwich to set off the scallops. (It also takes away the sting of that first bill...)