Ed's warning is well taken. I actually meant to leave that a bit thicker there.
You take a risk, both in turning it, and in selling it. I have dropped one of these pretty hard, and I was just sure I had chipped that thin area, but the cap is not very heavy, and acrylic is pretty strong. I've never done a Gentlemans though, so I am a bit worried. Thin material over a broader area? A bit scary.
Naturally, in selling this, I am trusting that my customer knows how to take care of things for which he's paid a good deal of money, and in the event of an accident, I will build him a new cap. Once only, and it will be thicker at that end :biggrin: (creating a de facto centerband). But I take the risk for the sake of the effect. That material is really amazing.
Also, if you try this, make sure, you have enough clearance between that thin end and the nib coupler ring, or one day you'll close the pen too hard, and that round shoulder on the ring will split that material.
Oh, and you'll need micro chisels to do this stuff.