There are many ways to post process a really cool metal print. You can do it by hand, with a tumbler, etc. Some great articles have been written so far about post-processing materials like bronzeFill, copperFill, brassFill & steelFill:
Polishing with some basic DYI-tools
https://learn.colorfabb.com/post-processing-gcreates-rocket-ship/
https://learn.colorfabb.com/teapot/
3Dhubs Talk on creating a Patina finish
https://www.3dhubs.com/talk/thread/bronzefill-patina-processing
Two articles by the Lulzbot team
https://www.lulzbot.com/learn/tutorials/accelerated-aging-your-metal-bearing-3d-prints
https://www.lulzbot.com/learn/tutorials/polishing-your-metal-bearing-3d-prints
One excellent blog by Nick Lievendag
http://nicklievendag.com/colorfabb-bronzefill-review/
Tony Short's colorFabb gift box and how he made it
https://learn.colorfabb.com/colorfabb-gift-box/
Adafruit's instructional video
Some interesting blog posts about prints not made by us (we did write the blogs, which is the easy job):
Ancient Greek Helmet by Andreas Mielonen: https://learn.colorfabb.com/helmet/
Fountain Pen by Rein van der Mast: https://learn.colorfabb.com/fountain-pen/
Huuuge Octolamp by Esteban Pacheco: https://learn.colorfabb.com/octolamp/
Please note: brassFill has been discontinued as per October 2018. More information: https://colorfabb.com/brassfill