I used the acid trick, works really well. I used a small Tupperware cup inside a big clear Tupperware bin. Put all the parts you want aged in the big clear bin, a few teaspoons of acid in the small cup and put it in the big bin. Seal the top of the big bin and wait 20 min or so and keep checking.
The metal will start to look like it’s sweating. Once the parts look sweaty enough you can take the parts out and let them sit overnight.
Check in the morning and they should look aged, slightly. If you want more “aged” put the parts in again 20-30 min. Then remove and leave overnight again.
It takes forever but if you rush it or leave the parts in to long, then take them out, the next day it may look like crap.
The biggest thing is cheap metal versus quality metal. I’ve always used fender American vintage parts so it takes forever. The cheaper stuff takes no time at all and will age quickly, so look for the metal sweating. If it looks soaked after a short time take it out.
Another thing is don’t wash the parts off with water. Just remove them and let them sit and air dry overnight. I didn’t sand or ruff any parts up prior.
The first pic is about 40 min and then overnight to air dry. Then I just take a old toothbrush with a bit of oil and rub it all over then rub that off. The second pic is avri gold hardware left in to long, still not bad but a heavy aged look.