Interesting, but honestly, I think I'd just have bought a couple of bottles of non-brewed condiment (39p in Tesco) and just soaked it in that.
Doesn't really work with the brass I have, or is way too slow. There is a slight bit of darkening after nearly two days...
The submerged bit is virtually untouched, but the bit above the surface has reacted well to the fumes (the cup was covered with cling film).
Dried off...
I like the verdigris part (should be Cupric Acetate). I'll have a poke at it later to see how robust it is.
I've already tried various things with vinegar, and didn't have much luck. With that, I was mostly after verdigris, and tried concoctions with vinegar and salt. In particular, I got a load of sawdust (cheap, in bags, for hamsters), got it moist with the solution, and put bits of brass in it. The idea was to simulate conditions underground, in organic material. The parts that were covered with the wetted sawdust got nothing - lack of oxygen, I reckon. When I cleared the sawdust away and exposed areas of the brass, the verdigris started to build. Sprinkling additional salt on it accelerated the build-up markedly, but it was very fractious - easily broke away to reveal clean brass underneath. Also tried sprinkling on Ammonium Chloride, but there wasn't much difference.
A few previous experiments...
The two at the top left were the ones in the wetted sawdust, one subsequently sprinkled with Sodium Chloride and the other with that and Ammonium Chloride. Thick build-up, and quite fractious. When scraped back with a bit of stick, the colour was very whitish. At top-right, patination solution No27 from some web site - a solution of Ammonium Chloride and Cupric Acetate. Very thin and pale, each new application seemed to wash away the previous one (you're supposed to build it up once a day or so). That's after 3 or 4 applications.
At bottom-left, just a splash of vinegar left for a couple of days or so (until it had all but evaporated). Like the dipped bit, some very slight darkening (less than it appears in the photo), and a hint of Cupric Acetate around the edge of the blob. At bottom-right, darkened first with the B&Q stripper, then a mix of commercial Cupric Acetate mixed with more stripper, left until the stripper had completely evaporated (no washing). Good texture and nicely robust, but the colour is too even. Not shown is another one like that with two differences - no darkening layer, and the cupric Acetate was as it came out of the jar, which was a bit granular. That was thicker and quite granular, much lighter in colour, and also robust. The one in the photo was a second attempt after grinding down the Cupric Acetate with a pestle and mortar.
So far, the latest bit with the vinegar fumes is looking the best for the verdigris patina, but I need to try it on a darkened bit first. Since I intend to add verdigris, I'm not too bothered about getting a nice even darkened finish for the 'underpainting'. I'm hoping to make the verdigris uneven (not sure how yet), and I want dark patches to show through where it's thin.
Anyway, after two days with the thicker application of the B&Q gloop, before washing...
Some blueness has appeared in the gloop, which washed off...
And a close-up of the edge on the other side, where some of the gloop worked its way round...
I've now applied the gloop to the front side and stuck it back in the chamber. This time, I brushed on a thin coat and then did the thicker one with be-gloved fingers right away. I did have a plan to dilute the stuff with a view to pouring a thin coating over the whole surface, but gave up after it didn't work with water, alcohol, and aliphatic hydrocarbon (Zest It oil paint thinner).
