How many individual castings? Did you cast the red, then turn; cast/turn the white; and then finally cast and turn the green? How many pen blanks did you get out of each stage?
I cast the red using a 10mm water pipe as a mould. Then, I set that red rod into a 15mm water pipe and filled it with white resin. Last, I sliced that white with red core and dropped the pieces into my 60x20x120 mould (I haven't documented it, but it's similar to the 7x blank mould I made
here) and cast it in green.
The result was 3 decent pen blanks and no waste.
Here's one of teh blanks rough cut and another turned and lightly polished.
You can't see it terribly well, but the topmost blanks are made from black rods cast into deep purple irridescent tubes cast into a black solid. Subtle, but they are going to make a real stonking set of executive pens.