What kinds of Unique Variants are possible? Is it possible to get a Sword Attack Speed Increase: High unique variant on a shield? Is it possible to get an Attack Speed Increase: High unique variant on a cutter? Is it possible to get a Gun Attack Speed Increase: High on a gunslinger sash?
I believe it's all explained fairly well on the wiki.
http://wiki.spiralknights.com/Unique_variants