So you want more weathering and oxidation?
Treat with freshly prepared KMnO solution as a spray and some H2O2 afterwards. Both are strong oxidizers and their effect is comparable to a couple years in the outdoors. KMnO breaks down rapidly because it reacts with everything except boron glass and some plastics. It's used to produce somewhat potable water in survival situations.
If you want, chlorine bleach will do the trick too. It turns copper shiny, and later flakey green. Chlorine is almost never easy on metals. But it can soak into untreated clay, so soaking/washing it out will be needed.
I know of several artists that work with these caustic materials to great advantage. I have seen and still own stunning copper patina art. As a potter, with some years of experience with raku and pit firing, there are many tricks to the trade I have seen and experienced. And to some results, especially those who do copper patina art, there is a certain amount of predictability, and that is great in those circumstances. I do not want that kind of control. Like raku and pit firing, I rather would guide the piece in a general direction and leave the rest to happenstance.
I didn't realize that my use of the word patina was going to reactive.
I think you pretty much have to be a potter to fully understand this.
Hypothetically, lets say you see 2 pots that you really like (and you may not). They have a rocky finish and are stone colored in various ways with subtle stains and discolorations.
Pot number one, says the potter, was sprayed with chemicals and strong oxidizers to achieve the look.
Pot number two, says the potter, was treated with natural metallic oxides and stains and buried in the earth for some time.
Now we have no way of knowing what these 2 pots look like in this hypothetical scenario, but let us assume that they are both pleasing to us in appearance. Neither way is the wrong way and certainly both can be appreciated equally, but........
Which would you get?
One size does not fit all..........