contaminations generally means rust mate
upon sand blasting, the surface will be extremely vulnerable to moisture, oil (from our skin), and other particles from the environment.
thats where the 4 hours window comes into play, so make sure you primed/coat it within the 4 hours window\

if you're looking for SA3 profile, an electric sander would help . you really don't have to go through the trouble of sand blasting them.

i have no prior experience with copper, but i can look it up for you.

would love to write more, but im currently out of town, letme get back to you once im back at my place

kudos for the black sparkle idea