Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

flame polishing is one way to make hazed plastic clear again, but it
depends on what you're working with.

Another way is to use a very dissolvable plastic and dip it in solvent and
let it dry. This works with acrylic and the stuff they make clear
screwdriver handles out of. I seal my name into handles like this with
acetone.